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 $86.25   7.631%   $92.8317   $92.83   $92.85   $92.80  
  Purchase #2 $53.83   3.206%   $55.5558   $55.56   $55.55   $55.60  
  Purchase #3 $54.39   11.323%   $60.5486   $60.55   $60.55   $60.50  
  Purchase #4 $137.50   13.403%   $155.9291   $155.93   $155.95   $155.90  
  Purchase #5 $238.79   4.688%   $249.9845   $249.98   $250.00   $250.00  
  Purchase #6 $5.82   8.111%   $6.2921   $6.29   $6.30   $6.30  
  Purchase #7 $138.55   6.662%   $147.7802   $147.78   $147.80   $147.80  
  7 purchase totals = $715.13       $768.9220   $768.92   $769.00   $768.90