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 $83.66   7.563%   $89.9872   $89.99   $90.00   $90.00  
  Purchase #2 $246.79   5.713%   $260.8891   $260.89   $260.90   $260.90  
  Purchase #3 $105.82   4.315%   $110.3861   $110.39   $110.40   $110.40  
  Purchase #4 $193.61   12.152%   $217.1375   $217.14   $217.15   $217.10  
  Purchase #5 $213.85   11.511%   $238.4663   $238.47   $238.45   $238.50  
  Purchase #6 $226.98   7.497%   $243.9967   $244.00   $244.00   $244.00  
  Purchase #7 $137.48   8.571%   $149.2634   $149.26   $149.25   $149.30  
  7 purchase totals = $1,208.19       $1,310.1263   $1,310.14   $1,310.15   $1,310.20