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 $215.25   8.216%   $232.9349   $232.93   $232.95   $232.90  
  Purchase #2 $122.66   6.441%   $130.5605   $130.56   $130.55   $130.60  
  Purchase #3 $113.37   7.738%   $122.1426   $122.14   $122.15   $122.10  
  Purchase #4 $226.27   12.372%   $254.2641   $254.26   $254.25   $254.30  
  Purchase #5 $152.73   7.722%   $164.5238   $164.52   $164.50   $164.50  
  Purchase #6 $195.31   10.275%   $215.3781   $215.38   $215.40   $215.40  
  Purchase #7 $238.89   7.620%   $257.0934   $257.09   $257.10   $257.10  
  7 purchase totals = $1,264.48       $1,376.8974   $1,376.88   $1,376.90   $1,376.90