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 $77.46   9.675%   $84.9543   $84.95   $84.95   $85.00  
  Purchase #2 $80.39   13.434%   $91.1896   $91.19   $91.20   $91.20  
  Purchase #3 $83.62   5.754%   $88.4315   $88.43   $88.45   $88.40  
  Purchase #4 $90.95   6.117%   $96.5134   $96.51   $96.50   $96.50  
  Purchase #5 $142.80   8.500%   $154.938   $154.94   $154.95   $154.90  
  Purchase #6 $94.52   12.460%   $106.2972   $106.30   $106.30   $106.30  
  Purchase #7 $204.57   12.264%   $229.6585   $229.66   $229.65   $229.70  
  7 purchase totals = $774.31       $851.9825   $851.98   $852.00   $852.00