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 $205.93   12.725%   $232.1346   $232.13   $232.15   $232.10  
  Purchase #2 $136.91   9.403%   $149.7836   $149.78   $149.80   $149.80  
  Purchase #3 $247.75   12.737%   $279.3059   $279.31   $279.30   $279.30  
  Purchase #4 $146.84   4.146%   $152.928   $152.93   $152.95   $152.90  
  Purchase #5 $55.75   8.189%   $60.3154   $60.32   $60.30   $60.30  
  Purchase #6 $96.99   3.872%   $100.7455   $100.75   $100.75   $100.70  
  Purchase #7 $48.85   4.346%   $50.973   $50.97   $50.95   $51.00  
  7 purchase totals = $939.02       $1,026.1860   $1,026.19   $1,026.20   $1,026.10