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 $214.47   11.327%   $238.763   $238.76   $238.75   $238.80  
  Purchase #2 $53.70   12.400%   $60.3588   $60.36   $60.35   $60.40  
  Purchase #3 $84.43   12.311%   $94.8242   $94.82   $94.80   $94.80  
  Purchase #4 $25.94   4.651%   $27.1465   $27.15   $27.15   $27.10  
  Purchase #5 $232.97   6.231%   $247.4864   $247.49   $247.50   $247.50  
  Purchase #6 $33.54   10.422%   $37.0355   $37.04   $37.05   $37.00  
  Purchase #7 $214.39   6.229%   $227.7444   $227.74   $227.75   $227.70  
  7 purchase totals = $859.44       $933.3588   $933.36   $933.35   $933.30