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 $119.55   5.498%   $126.1229   $126.12   $126.10   $126.10  
  Purchase #2 $43.37   5.763%   $45.8694   $45.87   $45.85   $45.90  
  Purchase #3 $110.66   12.232%   $124.1959   $124.20   $124.20   $124.20  
  Purchase #4 $144.55   6.220%   $153.541   $153.54   $153.55   $153.50  
  Purchase #5 $95.66   13.580%   $108.6506   $108.65   $108.65   $108.70  
  Purchase #6 $51.36   11.469%   $57.2505   $57.25   $57.25   $57.30  
  Purchase #7 $61.68   5.804%   $65.2599   $65.26   $65.25   $65.30  
  7 purchase totals = $626.83       $680.8902   $680.89   $680.85   $681.00