Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $205.89   11.205%   $228.96   $228.96   $228.95   $229.00  
  Purchase #2 $223.35   13.829%   $254.2371   $254.24   $254.25   $254.20  
  Purchase #3 $153.51   13.743%   $174.6069   $174.61   $174.60   $174.60  
  Purchase #4 $209.66   12.547%   $235.966   $235.97   $235.95   $236.00  
  Purchase #5 $154.95   12.210%   $173.8694   $173.87   $173.85   $173.90  
  Purchase #6 $169.61   10.769%   $187.8753   $187.88   $187.90   $187.90  
  Purchase #7 $181.51   5.226%   $190.9957   $191.00   $191.00   $191.00  
  7 purchase totals = $1,298.48       $1,446.5104   $1,446.53   $1,446.50   $1,446.60