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 $248.65   9.320%   $271.8242   $271.82   $271.80   $271.80  
  Purchase #2 $85.39   13.648%   $97.044   $97.04   $97.05   $97.00  
  Purchase #3 $54.76   7.187%   $58.6956   $58.70   $58.70   $58.70  
  Purchase #4 $160.56   5.414%   $169.2527   $169.25   $169.25   $169.30  
  Purchase #5 $180.99   12.545%   $203.6952   $203.70   $203.70   $203.70  
  Purchase #6 $55.66   11.412%   $62.0119   $62.01   $62.00   $62.00  
  Purchase #7 $82.48   10.391%   $91.0505   $91.05   $91.05   $91.10  
  7 purchase totals = $868.49       $953.5741   $953.57   $953.55   $953.60