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 $58.99   13.310%   $66.8416   $66.84   $66.85   $66.80  
  Purchase #2 $191.98   11.460%   $213.9809   $213.98   $214.00   $214.00  
  Purchase #3 $224.43   12.831%   $253.2266   $253.23   $253.25   $253.20  
  Purchase #4 $23.91   8.566%   $25.9581   $25.96   $25.95   $26.00  
  Purchase #5 $94.60   5.641%   $99.9364   $99.94   $99.95   $99.90  
  Purchase #6 $84.75   5.839%   $89.6986   $89.70   $89.70   $89.70  
  Purchase #7 $162.76   8.216%   $176.1324   $176.13   $176.15   $176.10  
  7 purchase totals = $841.42       $925.7746   $925.78   $925.85   $925.70