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 $229.70   7.166%   $246.1603   $246.16   $246.15   $246.20  
  Purchase #2 $58.49   6.739%   $62.4316   $62.43   $62.45   $62.40  
  Purchase #3 $118.98   6.176%   $126.3282   $126.33   $126.35   $126.30  
  Purchase #4 $117.60   4.427%   $122.8062   $122.81   $122.80   $122.80  
  Purchase #5 $228.81   3.110%   $235.926   $235.93   $235.95   $235.90  
  Purchase #6 $162.68   6.222%   $172.8019   $172.80   $172.80   $172.80  
  Purchase #7 $8.68   5.797%   $9.1832   $9.18   $9.20   $9.20  
  7 purchase totals = $924.94       $975.6374   $975.64   $975.70   $975.60