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 $58.74   13.557%   $66.7034   $66.70   $66.70   $66.70  
  Purchase #2 $85.99   10.422%   $94.9519   $94.95   $94.95   $95.00  
  Purchase #3 $196.76   11.441%   $219.2713   $219.27   $219.25   $219.30  
  Purchase #4 $147.77   12.309%   $165.959   $165.96   $165.95   $166.00  
  Purchase #5 $213.74   11.243%   $237.7708   $237.77   $237.75   $237.80  
  Purchase #6 $124.69   10.399%   $137.6565   $137.66   $137.65   $137.70  
  Purchase #7 $69.54   13.435%   $78.8827   $78.88   $78.90   $78.90  
  7 purchase totals = $897.23       $1,001.1956   $1,001.19   $1,001.15   $1,001.40