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 $51.96   3.461%   $53.7583   $53.76   $53.75   $53.80  
  Purchase #2 $195.47   6.552%   $208.2772   $208.28   $208.30   $208.30  
  Purchase #3 $243.44   11.406%   $271.2068   $271.21   $271.20   $271.20  
  Purchase #4 $167.33   8.363%   $181.3238   $181.32   $181.30   $181.30  
  Purchase #5 $34.59   6.859%   $36.9625   $36.96   $36.95   $37.00  
  Purchase #6 $22.95   3.214%   $23.6876   $23.69   $23.70   $23.70  
  Purchase #7 $65.35   5.173%   $68.7306   $68.73   $68.75   $68.70  
  7 purchase totals = $781.09       $843.9468   $843.95   $843.95   $844.00