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 $48.29   8.383%   $52.3382   $52.34   $52.35   $52.30  
  Purchase #2 $59.71   4.410%   $62.3432   $62.34   $62.35   $62.30  
  Purchase #3 $118.60   3.793%   $123.0985   $123.10   $123.10   $123.10  
  Purchase #4 $213.56   13.852%   $243.1423   $243.14   $243.15   $243.10  
  Purchase #5 $209.28   10.466%   $231.1832   $231.18   $231.20   $231.20  
  Purchase #6 $209.85   4.472%   $219.2345   $219.23   $219.25   $219.20  
  Purchase #7 $33.26   4.559%   $34.7763   $34.78   $34.80   $34.80  
  7 purchase totals = $892.55       $966.1162   $966.11   $966.20   $966.00