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 $53.36   11.232%   $59.3534   $59.35   $59.35   $59.40  
  Purchase #2 $196.52   8.831%   $213.8747   $213.87   $213.85   $213.90  
  Purchase #3 $90.62   12.765%   $102.1876   $102.19   $102.20   $102.20  
  Purchase #4 $40.27   10.752%   $44.5998   $44.60   $44.60   $44.60  
  Purchase #5 $174.82   6.577%   $186.3179   $186.32   $186.30   $186.30  
  Purchase #6 $162.73   4.623%   $170.253   $170.25   $170.25   $170.30  
  Purchase #7 $109.74   9.612%   $120.2882   $120.29   $120.30   $120.30  
  7 purchase totals = $828.06       $896.8746   $896.87   $896.85   $897.00