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 $44.66   3.846%   $46.3776   $46.38   $46.40   $46.40  
  Purchase #2 $83.41   12.451%   $93.7954   $93.80   $93.80   $93.80  
  Purchase #3 $130.35   4.533%   $136.2588   $136.26   $136.25   $136.30  
  Purchase #4 $161.52   3.671%   $167.4494   $167.45   $167.45   $167.40  
  Purchase #5 $213.50   11.565%   $238.1913   $238.19   $238.20   $238.20  
  Purchase #6 $191.79   6.664%   $204.5709   $204.57   $204.55   $204.60  
  Purchase #7 $12.25   9.651%   $13.4322   $13.43   $13.45   $13.40  
  7 purchase totals = $837.48       $900.0756   $900.08   $900.10   $900.10