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 $186.84   11.680%   $208.6629   $208.66   $208.65   $208.70  
  Purchase #2 $154.51   9.778%   $169.618   $169.62   $169.60   $169.60  
  Purchase #3 $15.93   7.230%   $17.0817   $17.08   $17.10   $17.10  
  Purchase #4 $220.65   7.540%   $237.287   $237.29   $237.30   $237.30  
  Purchase #5 $49.89   7.128%   $53.4462   $53.45   $53.45   $53.40  
  Purchase #6 $19.96   4.659%   $20.8899   $20.89   $20.90   $20.90  
  Purchase #7 $49.31   9.781%   $54.133   $54.13   $54.15   $54.10  
  7 purchase totals = $697.09       $761.1187   $761.12   $761.15   $761.10