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 $61.78   8.489%   $67.0245   $67.02   $67.00   $67.00  
  Purchase #2 $154.40   10.488%   $170.5935   $170.59   $170.60   $170.60  
  Purchase #3 $81.99   12.206%   $91.9977   $92.00   $92.00   $92.00  
  Purchase #4 $228.30   3.442%   $236.1581   $236.16   $236.15   $236.20  
  Purchase #5 $53.52   9.863%   $58.7987   $58.80   $58.80   $58.80  
  Purchase #6 $237.31   12.309%   $266.5205   $266.52   $266.50   $266.50  
  Purchase #7 $168.35   5.110%   $176.9527   $176.95   $176.95   $177.00  
  7 purchase totals = $985.65       $1,068.0457   $1,068.04   $1,068.00   $1,068.10