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 $168.48   13.720%   $191.5955   $191.60   $191.60   $191.60  
  Purchase #2 $169.53   11.804%   $189.5413   $189.54   $189.55   $189.50  
  Purchase #3 $62.62   9.639%   $68.6559   $68.66   $68.65   $68.70  
  Purchase #4 $249.65   10.188%   $275.0843   $275.08   $275.10   $275.10  
  Purchase #5 $183.65   11.764%   $205.2546   $205.25   $205.25   $205.30  
  Purchase #6 $17.98   9.307%   $19.6534   $19.65   $19.65   $19.70  
  Purchase #7 $62.66   13.116%   $70.8785   $70.88   $70.90   $70.90  
  7 purchase totals = $914.57       $1,020.6635   $1,020.66   $1,020.70   $1,020.80