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 $217.67   12.264%   $244.365   $244.37   $244.35   $244.40  
  Purchase #2 $16.27   8.171%   $17.5994   $17.60   $17.60   $17.60  
  Purchase #3 $42.53   3.599%   $44.0607   $44.06   $44.05   $44.10  
  Purchase #4 $37.75   5.649%   $39.8825   $39.88   $39.90   $39.90  
  Purchase #5 $56.73   10.485%   $62.6781   $62.68   $62.70   $62.70  
  Purchase #6 $90.57   7.179%   $97.072   $97.07   $97.05   $97.10  
  Purchase #7 $40.95   9.772%   $44.9516   $44.95   $44.95   $45.00  
  7 purchase totals = $502.47       $550.6093   $550.61   $550.60   $550.80