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 $59.34   10.254%   $65.4247   $65.42   $65.40   $65.40  
  Purchase #2 $206.82   8.714%   $224.8423   $224.84   $224.85   $224.80  
  Purchase #3 $23.85   8.599%   $25.9009   $25.90   $25.90   $25.90  
  Purchase #4 $149.76   13.457%   $169.9132   $169.91   $169.90   $169.90  
  Purchase #5 $15.97   11.847%   $17.862   $17.86   $17.85   $17.90  
  Purchase #6 $54.96   11.603%   $61.337   $61.34   $61.35   $61.30  
  Purchase #7 $186.56   12.331%   $209.5647   $209.56   $209.55   $209.60  
  7 purchase totals = $697.26       $774.8448   $774.83   $774.80   $774.80