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 $113.97   10.258%   $125.661   $125.66   $125.65   $125.70  
  Purchase #2 $39.75   7.138%   $42.5874   $42.59   $42.60   $42.60  
  Purchase #3 $191.69   7.573%   $206.2067   $206.21   $206.20   $206.20  
  Purchase #4 $166.92   5.160%   $175.5331   $175.53   $175.55   $175.50  
  Purchase #5 $194.50   11.182%   $216.249   $216.25   $216.25   $216.20  
  Purchase #6 $109.51   6.772%   $116.926   $116.93   $116.95   $116.90  
  Purchase #7 $34.36   6.395%   $36.5573   $36.56   $36.55   $36.60  
  7 purchase totals = $850.70       $919.7205   $919.73   $919.75   $919.70