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 $63.83   5.277%   $67.1983   $67.20   $67.20   $67.20  
  Purchase #2 $109.81   3.717%   $113.8916   $113.89   $113.90   $113.90  
  Purchase #3 $40.52   11.129%   $45.0295   $45.03   $45.05   $45.00  
  Purchase #4 $218.40   6.128%   $231.7836   $231.78   $231.80   $231.80  
  Purchase #5 $238.57   11.250%   $265.4091   $265.41   $265.40   $265.40  
  Purchase #6 $31.30   6.144%   $33.2231   $33.22   $33.20   $33.20  
  Purchase #7 $182.56   9.263%   $199.4705   $199.47   $199.45   $199.50  
  7 purchase totals = $884.99       $956.0057   $956.00   $956.00   $956.00