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 $141.34   8.125%   $152.8239   $152.82   $152.80   $152.80  
  Purchase #2 $101.43   8.572%   $110.1246   $110.12   $110.10   $110.10  
  Purchase #3 $218.66   6.581%   $233.05   $233.05   $233.05   $233.10  
  Purchase #4 $100.88   10.137%   $111.1062   $111.11   $111.10   $111.10  
  Purchase #5 $222.70   4.252%   $232.1692   $232.17   $232.15   $232.20  
  Purchase #6 $57.73   11.781%   $64.5312   $64.53   $64.55   $64.50  
  Purchase #7 $86.44   8.181%   $93.5117   $93.51   $93.50   $93.50  
  7 purchase totals = $929.18       $997.3168   $997.31   $997.25   $997.30