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 $119.60   10.305%   $131.9248   $131.92   $131.90   $131.90  
  Purchase #2 $181.52   6.728%   $193.7327   $193.73   $193.75   $193.70  
  Purchase #3 $47.82   3.795%   $49.6348   $49.63   $49.65   $49.60  
  Purchase #4 $166.74   11.420%   $185.7817   $185.78   $185.80   $185.80  
  Purchase #5 $167.51   13.369%   $189.9044   $189.90   $189.90   $189.90  
  Purchase #6 $137.92   9.133%   $150.5162   $150.52   $150.50   $150.50  
  Purchase #7 $68.98   7.259%   $73.9873   $73.99   $74.00   $74.00  
  7 purchase totals = $890.09       $975.4819   $975.47   $975.50   $975.40