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 $236.33   6.594%   $251.9136   $251.91   $251.90   $251.90  
  Purchase #2 $152.93   10.710%   $169.3088   $169.31   $169.30   $169.30  
  Purchase #3 $95.94   10.394%   $105.912   $105.91   $105.90   $105.90  
  Purchase #4 $211.44   11.395%   $235.5336   $235.53   $235.55   $235.50  
  Purchase #5 $87.27   8.798%   $94.948   $94.95   $94.95   $94.90  
  Purchase #6 $225.45   13.846%   $256.6658   $256.67   $256.65   $256.70  
  Purchase #7 $76.42   10.106%   $84.143   $84.14   $84.15   $84.10  
  7 purchase totals = $1,085.78       $1,198.4248   $1,198.42   $1,198.40   $1,198.30