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 $131.88   7.545%   $141.8303   $141.83   $141.85   $141.80  
  Purchase #2 $17.81   11.797%   $19.911   $19.91   $19.90   $19.90  
  Purchase #3 $64.28   9.708%   $70.5203   $70.52   $70.50   $70.50  
  Purchase #4 $156.45   7.331%   $167.9193   $167.92   $167.90   $167.90  
  Purchase #5 $194.97   3.208%   $201.2246   $201.22   $201.20   $201.20  
  Purchase #6 $140.32   12.564%   $157.9498   $157.95   $157.95   $157.90  
  Purchase #7 $245.58   12.699%   $276.7662   $276.77   $276.75   $276.80  
  7 purchase totals = $951.29       $1,036.1215   $1,036.12   $1,036.05   $1,036.00