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 $52.39   9.451%   $57.3414   $57.34   $57.35   $57.30  
  Purchase #2 $148.41   8.508%   $161.0367   $161.04   $161.05   $161.00  
  Purchase #3 $50.43   13.639%   $57.3081   $57.31   $57.30   $57.30  
  Purchase #4 $101.64   4.866%   $106.5858   $106.59   $106.60   $106.60  
  Purchase #5 $50.63   6.844%   $54.0951   $54.10   $54.10   $54.10  
  Purchase #6 $216.48   6.853%   $231.3154   $231.32   $231.30   $231.30  
  Purchase #7 $195.87   3.112%   $201.9655   $201.97   $201.95   $202.00  
  7 purchase totals = $815.85       $869.6480   $869.67   $869.65   $869.60