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 $52.46   12.383%   $58.9561   $58.96   $58.95   $59.00  
  Purchase #2 $87.79   10.684%   $97.1695   $97.17   $97.15   $97.20  
  Purchase #3 $79.94   6.279%   $84.9594   $84.96   $84.95   $85.00  
  Purchase #4 $78.70   7.816%   $84.8512   $84.85   $84.85   $84.90  
  Purchase #5 $168.30   3.513%   $174.2124   $174.21   $174.20   $174.20  
  Purchase #6 $153.79   8.425%   $166.7468   $166.75   $166.75   $166.70  
  Purchase #7 $162.84   12.375%   $182.9915   $182.99   $183.00   $183.00  
  7 purchase totals = $783.82       $849.8869   $849.89   $849.85   $850.00