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 $143.50   5.123%   $150.8515   $150.85   $150.85   $150.90  
  Purchase #2 $25.39   10.166%   $27.9711   $27.97   $27.95   $28.00  
  Purchase #3 $177.50   13.420%   $201.3205   $201.32   $201.30   $201.30  
  Purchase #4 $189.60   9.648%   $207.8926   $207.89   $207.90   $207.90  
  Purchase #5 $229.41   11.559%   $255.9275   $255.93   $255.95   $255.90  
  Purchase #6 $10.35   4.272%   $10.7922   $10.79   $10.80   $10.80  
  Purchase #7 $8.90   10.739%   $9.8558   $9.86   $9.85   $9.90  
  7 purchase totals = $784.65       $864.6112   $864.61   $864.60   $864.70