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 $53.35   6.496%   $56.8156   $56.82   $56.80   $56.80  
  Purchase #2 $57.31   12.184%   $64.2927   $64.29   $64.30   $64.30  
  Purchase #3 $219.44   6.344%   $233.3613   $233.36   $233.35   $233.40  
  Purchase #4 $159.31   3.549%   $164.9639   $164.96   $164.95   $165.00  
  Purchase #5 $61.76   3.771%   $64.089   $64.09   $64.10   $64.10  
  Purchase #6 $224.75   10.686%   $248.7668   $248.77   $248.75   $248.80  
  Purchase #7 $144.26   10.525%   $159.4434   $159.44   $159.45   $159.40  
  7 purchase totals = $920.18       $991.7327   $991.73   $991.70   $991.80