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 $49.71   8.112%   $53.7425   $53.74   $53.75   $53.70  
  Purchase #2 $212.87   5.575%   $224.7375   $224.74   $224.75   $224.70  
  Purchase #3 $111.50   7.461%   $119.819   $119.82   $119.80   $119.80  
  Purchase #4 $149.96   11.746%   $167.5743   $167.57   $167.55   $167.60  
  Purchase #5 $165.84   4.865%   $173.9081   $173.91   $173.90   $173.90  
  Purchase #6 $88.56   9.593%   $97.0556   $97.06   $97.05   $97.10  
  Purchase #7 $135.56   10.444%   $149.7179   $149.72   $149.70   $149.70  
  7 purchase totals = $914.00       $986.5549   $986.56   $986.50   $986.50