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 $244.75   9.217%   $267.3086   $267.31   $267.30   $267.30  
  Purchase #2 $79.34   9.150%   $86.5996   $86.60   $86.60   $86.60  
  Purchase #3 $53.42   4.373%   $55.7561   $55.76   $55.75   $55.80  
  Purchase #4 $168.86   5.165%   $177.5816   $177.58   $177.60   $177.60  
  Purchase #5 $64.49   10.238%   $71.0925   $71.09   $71.10   $71.10  
  Purchase #6 $72.42   3.255%   $74.7773   $74.78   $74.80   $74.80  
  Purchase #7 $44.49   9.772%   $48.8376   $48.84   $48.85   $48.80  
  7 purchase totals = $727.77       $781.9533   $781.96   $782.00   $782.00