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 $141.72   6.605%   $151.0806   $151.08   $151.10   $151.10  
  Purchase #2 $244.99   7.852%   $264.2266   $264.23   $264.25   $264.20  
  Purchase #3 $137.77   4.616%   $144.1295   $144.13   $144.15   $144.10  
  Purchase #4 $208.87   13.403%   $236.8648   $236.86   $236.85   $236.90  
  Purchase #5 $242.43   6.210%   $257.4849   $257.48   $257.50   $257.50  
  Purchase #6 $119.52   13.731%   $135.9313   $135.93   $135.95   $135.90  
  Purchase #7 $68.77   9.170%   $75.0762   $75.08   $75.10   $75.10  
  7 purchase totals = $1,164.07       $1,264.7939   $1,264.79   $1,264.90   $1,264.80