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 $222.41   8.512%   $241.3415   $241.34   $241.35   $241.30  
  Purchase #2 $60.52   9.613%   $66.3378   $66.34   $66.35   $66.30  
  Purchase #3 $175.83   7.464%   $188.954   $188.95   $188.95   $189.00  
  Purchase #4 $171.28   3.779%   $177.7527   $177.75   $177.75   $177.80  
  Purchase #5 $164.66   11.260%   $183.2007   $183.20   $183.20   $183.20  
  Purchase #6 $132.41   4.568%   $138.4585   $138.46   $138.45   $138.50  
  Purchase #7 $236.29   3.133%   $243.693   $243.69   $243.70   $243.70  
  7 purchase totals = $1,163.40       $1,239.7382   $1,239.73   $1,239.75   $1,239.80