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 $154.46   12.229%   $173.3489   $173.35   $173.35   $173.30  
  Purchase #2 $213.26   11.261%   $237.2752   $237.28   $237.30   $237.30  
  Purchase #3 $208.72   10.659%   $230.9675   $230.97   $230.95   $231.00  
  Purchase #4 $237.66   3.174%   $245.2033   $245.20   $245.20   $245.20  
  Purchase #5 $206.57   13.605%   $234.6738   $234.67   $234.65   $234.70  
  Purchase #6 $15.40   9.358%   $16.8411   $16.84   $16.85   $16.80  
  Purchase #7 $95.52   9.820%   $104.9001   $104.90   $104.90   $104.90  
  7 purchase totals = $1,131.59       $1,243.2099   $1,243.21   $1,243.20   $1,243.20