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 $96.51   3.581%   $99.966   $99.97   $99.95   $100.00  
  Purchase #2 $240.90   12.613%   $271.2847   $271.28   $271.30   $271.30  
  Purchase #3 $229.98   6.651%   $245.276   $245.28   $245.30   $245.30  
  Purchase #4 $58.41   10.581%   $64.5904   $64.59   $64.60   $64.60  
  Purchase #5 $151.65   5.184%   $159.5115   $159.51   $159.50   $159.50  
  Purchase #6 $125.83   9.531%   $137.8229   $137.82   $137.80   $137.80  
  Purchase #7 $71.92   4.666%   $75.2758   $75.28   $75.30   $75.30  
  7 purchase totals = $975.20       $1,053.7273   $1,053.73   $1,053.75   $1,053.80