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 $175.78   10.319%   $193.9187   $193.92   $193.90   $193.90  
  Purchase #2 $177.81   11.171%   $197.6732   $197.67   $197.65   $197.70  
  Purchase #3 $226.32   8.365%   $245.2517   $245.25   $245.25   $245.30  
  Purchase #4 $150.92   10.660%   $167.0081   $167.01   $167.00   $167.00  
  Purchase #5 $122.65   12.833%   $138.3897   $138.39   $138.40   $138.40  
  Purchase #6 $55.99   7.127%   $59.9804   $59.98   $60.00   $60.00  
  Purchase #7 $140.41   6.637%   $149.729   $149.73   $149.75   $149.70  
  7 purchase totals = $1,049.88       $1,151.9508   $1,151.95   $1,151.95   $1,152.00