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 $55.59   6.654%   $59.289   $59.29   $59.30   $59.30  
  Purchase #2 $184.97   6.860%   $197.6589   $197.66   $197.65   $197.70  
  Purchase #3 $71.57   11.214%   $79.5959   $79.60   $79.60   $79.60  
  Purchase #4 $106.34   4.159%   $110.7627   $110.76   $110.75   $110.80  
  Purchase #5 $211.63   8.305%   $229.2059   $229.21   $229.20   $229.20  
  Purchase #6 $132.39   13.238%   $149.9158   $149.92   $149.90   $149.90  
  Purchase #7 $123.54   4.184%   $128.7089   $128.71   $128.70   $128.70  
  7 purchase totals = $886.03       $955.1371   $955.15   $955.10   $955.20