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 $90.41   8.791%   $98.3579   $98.36   $98.35   $98.40  
  Purchase #2 $235.69   3.558%   $244.0759   $244.08   $244.10   $244.10  
  Purchase #3 $151.44   3.556%   $156.8252   $156.83   $156.85   $156.80  
  Purchase #4 $225.68   4.249%   $235.2691   $235.27   $235.25   $235.30  
  Purchase #5 $87.84   9.406%   $96.1022   $96.10   $96.10   $96.10  
  Purchase #6 $203.97   8.537%   $221.3829   $221.38   $221.40   $221.40  
  Purchase #7 $48.56   6.342%   $51.6397   $51.64   $51.65   $51.60  
  7 purchase totals = $1,043.59       $1,103.6529   $1,103.66   $1,103.70   $1,103.70