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 $67.63   12.422%   $76.031   $76.03   $76.05   $76.00  
  Purchase #2 $58.78   13.417%   $66.6665   $66.67   $66.65   $66.70  
  Purchase #3 $191.29   5.572%   $201.9487   $201.95   $201.95   $201.90  
  Purchase #4 $141.39   7.235%   $151.6196   $151.62   $151.60   $151.60  
  Purchase #5 $164.97   10.236%   $181.8563   $181.86   $181.85   $181.90  
  Purchase #6 $90.50   6.657%   $96.5246   $96.52   $96.50   $96.50  
  Purchase #7 $96.59   9.853%   $106.107   $106.11   $106.10   $106.10  
  7 purchase totals = $811.15       $880.7537   $880.76   $880.70   $880.70