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 $65.94   11.764%   $73.6972   $73.70   $73.70   $73.70  
  Purchase #2 $114.39   8.755%   $124.4048   $124.40   $124.40   $124.40  
  Purchase #3 $179.56   7.495%   $193.018   $193.02   $193.00   $193.00  
  Purchase #4 $111.35   10.231%   $122.7422   $122.74   $122.75   $122.70  
  Purchase #5 $119.27   13.503%   $135.375   $135.38   $135.40   $135.40  
  Purchase #6 $47.34   10.636%   $52.3751   $52.38   $52.40   $52.40  
  Purchase #7 $206.97   10.374%   $228.4411   $228.44   $228.45   $228.40  
  7 purchase totals = $844.82       $930.0534   $930.06   $930.10   $930.00