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 $233.39   13.793%   $265.5815   $265.58   $265.60   $265.60  
  Purchase #2 $132.41   3.604%   $137.1821   $137.18   $137.20   $137.20  
  Purchase #3 $62.26   3.821%   $64.639   $64.64   $64.65   $64.60  
  Purchase #4 $135.45   11.496%   $151.0213   $151.02   $151.00   $151.00  
  Purchase #5 $215.42   11.410%   $239.9994   $240.00   $240.00   $240.00  
  Purchase #6 $231.29   5.413%   $243.8097   $243.81   $243.80   $243.80  
  Purchase #7 $212.83   7.307%   $228.3815   $228.38   $228.40   $228.40  
  7 purchase totals = $1,223.05       $1,330.6145   $1,330.61   $1,330.65   $1,330.60