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 $85.56   10.247%   $94.3273   $94.33   $94.35   $94.30  
  Purchase #2 $178.78   6.301%   $190.0449   $190.04   $190.05   $190.00  
  Purchase #3 $215.52   9.784%   $236.6065   $236.61   $236.60   $236.60  
  Purchase #4 $61.69   5.280%   $64.9472   $64.95   $64.95   $64.90  
  Purchase #5 $97.29   7.554%   $104.6393   $104.64   $104.65   $104.60  
  Purchase #6 $45.29   5.387%   $47.7298   $47.73   $47.75   $47.70  
  Purchase #7 $226.95   13.366%   $257.2841   $257.28   $257.30   $257.30  
  7 purchase totals = $911.08       $995.5791   $995.58   $995.65   $995.40