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 $119.98   5.794%   $126.9316   $126.93   $126.95   $126.90  
  Purchase #2 $246.64   12.398%   $277.2184   $277.22   $277.20   $277.20  
  Purchase #3 $94.93   4.393%   $99.1003   $99.10   $99.10   $99.10  
  Purchase #4 $160.60   5.227%   $168.9946   $168.99   $169.00   $169.00  
  Purchase #5 $102.40   4.231%   $106.7325   $106.73   $106.75   $106.70  
  Purchase #6 $75.73   5.614%   $79.9815   $79.98   $80.00   $80.00  
  Purchase #7 $180.72   4.322%   $188.5307   $188.53   $188.55   $188.50  
  7 purchase totals = $981.00       $1,047.4896   $1,047.48   $1,047.55   $1,047.40