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 $70.66   3.523%   $73.1494   $73.15   $73.15   $73.10  
  Purchase #2 $134.96   12.425%   $151.7288   $151.73   $151.75   $151.70  
  Purchase #3 $118.26   7.173%   $126.7428   $126.74   $126.75   $126.70  
  Purchase #4 $185.49   6.696%   $197.9104   $197.91   $197.90   $197.90  
  Purchase #5 $125.48   11.251%   $139.5978   $139.60   $139.60   $139.60  
  Purchase #6 $196.99   6.837%   $210.4582   $210.46   $210.45   $210.50  
  Purchase #7 $116.53   3.496%   $120.6039   $120.60   $120.60   $120.60  
  7 purchase totals = $948.37       $1,020.1913   $1,020.19   $1,020.20   $1,020.10