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 $54.38   10.208%   $59.9311   $59.93   $59.95   $59.90  
  Purchase #2 $151.41   11.653%   $169.0538   $169.05   $169.05   $169.10  
  Purchase #3 $113.93   4.626%   $119.2004   $119.20   $119.20   $119.20  
  Purchase #4 $229.30   5.253%   $241.3451   $241.35   $241.35   $241.30  
  Purchase #5 $80.36   5.774%   $85   $85.00   $85.00   $85.00  
  Purchase #6 $76.49   9.594%   $83.8285   $83.83   $83.85   $83.80  
  Purchase #7 $91.99   6.431%   $97.9059   $97.91   $97.90   $97.90  
  7 purchase totals = $797.86       $856.2648   $856.27   $856.30   $856.20