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 $114.46   9.220%   $125.0132   $125.01   $125.00   $125.00  
  Purchase #2 $165.27   13.281%   $187.2195   $187.22   $187.20   $187.20  
  Purchase #3 $218.75   6.535%   $233.0453   $233.05   $233.05   $233.00  
  Purchase #4 $207.82   3.684%   $215.4761   $215.48   $215.50   $215.50  
  Purchase #5 $61.35   9.122%   $66.9463   $66.95   $66.95   $66.90  
  Purchase #6 $43.61   6.816%   $46.5825   $46.58   $46.60   $46.60  
  Purchase #7 $58.72   8.527%   $63.7271   $63.73   $63.75   $63.70  
  7 purchase totals = $869.98       $938.0100   $938.02   $938.05   $937.90