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 $41.35   8.561%   $44.89   $44.89   $44.90   $44.90  
  Purchase #2 $182.84   11.677%   $204.1902   $204.19   $204.20   $204.20  
  Purchase #3 $200.60   12.106%   $224.8846   $224.88   $224.90   $224.90  
  Purchase #4 $153.86   5.648%   $162.55   $162.55   $162.55   $162.60  
  Purchase #5 $91.37   6.698%   $97.49   $97.49   $97.50   $97.50  
  Purchase #6 $110.99   11.406%   $123.6495   $123.65   $123.65   $123.60  
  Purchase #7 $145.63   9.578%   $159.5784   $159.58   $159.60   $159.60  
  7 purchase totals = $926.64       $1,017.2327   $1,017.23   $1,017.30   $1,017.30