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 $244.97   9.417%   $268.0388   $268.04   $268.05   $268.00  
  Purchase #2 $138.72   4.505%   $144.9693   $144.97   $144.95   $145.00  
  Purchase #3 $46.35   12.514%   $52.1502   $52.15   $52.15   $52.20  
  Purchase #4 $159.88   5.804%   $169.1594   $169.16   $169.15   $169.20  
  Purchase #5 $218.46   12.803%   $246.4294   $246.43   $246.45   $246.40  
  Purchase #6 $62.82   10.817%   $69.6152   $69.62   $69.60   $69.60  
  Purchase #7 $74.91   6.727%   $79.9492   $79.95   $79.95   $79.90  
  7 purchase totals = $946.11       $1,030.3115   $1,030.32   $1,030.30   $1,030.30