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 $88.26   9.593%   $96.7268   $96.73   $96.75   $96.70  
  Purchase #2 $201.60   4.257%   $210.1821   $210.18   $210.20   $210.20  
  Purchase #3 $112.60   13.224%   $127.4902   $127.49   $127.50   $127.50  
  Purchase #4 $222.54   5.574%   $234.9444   $234.94   $234.95   $234.90  
  Purchase #5 $41.87   10.489%   $46.2617   $46.26   $46.25   $46.30  
  Purchase #6 $184.54   9.836%   $202.6914   $202.69   $202.70   $202.70  
  Purchase #7 $36.85   6.413%   $39.2132   $39.21   $39.20   $39.20  
  7 purchase totals = $888.26       $957.5098   $957.50   $957.55   $957.50