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 $226.25   8.807%   $246.1758   $246.18   $246.20   $246.20  
  Purchase #2 $68.83   3.570%   $71.2872   $71.29   $71.30   $71.30  
  Purchase #3 $34.28   7.402%   $36.8174   $36.82   $36.80   $36.80  
  Purchase #4 $228.84   8.809%   $248.9985   $249.00   $249.00   $249.00  
  Purchase #5 $44.74   3.175%   $46.1605   $46.16   $46.15   $46.20  
  Purchase #6 $229.61   6.447%   $244.413   $244.41   $244.40   $244.40  
  Purchase #7 $108.57   3.407%   $112.269   $112.27   $112.25   $112.30  
  7 purchase totals = $941.12       $1,006.1214   $1,006.13   $1,006.10   $1,006.20