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 $197.97   13.237%   $224.1753   $224.18   $224.20   $224.20  
  Purchase #2 $60.34   10.108%   $66.4392   $66.44   $66.45   $66.40  
  Purchase #3 $64.99   4.613%   $67.988   $67.99   $68.00   $68.00  
  Purchase #4 $223.77   5.662%   $236.4399   $236.44   $236.45   $236.40  
  Purchase #5 $106.77   12.457%   $120.0703   $120.07   $120.05   $120.10  
  Purchase #6 $90.92   11.861%   $101.704   $101.70   $101.70   $101.70  
  Purchase #7 $103.64   12.736%   $116.8396   $116.84   $116.85   $116.80  
  7 purchase totals = $848.40       $933.6563   $933.66   $933.70   $933.60