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 $70.98   3.273%   $73.3032   $73.30   $73.30   $73.30  
  Purchase #2 $110.83   7.277%   $118.8951   $118.90   $118.90   $118.90  
  Purchase #3 $82.88   7.344%   $88.9667   $88.97   $88.95   $89.00  
  Purchase #4 $179.57   3.337%   $185.5623   $185.56   $185.55   $185.60  
  Purchase #5 $107.28   9.740%   $117.7291   $117.73   $117.75   $117.70  
  Purchase #6 $26.89   4.154%   $28.007   $28.01   $28.00   $28.00  
  Purchase #7 $105.26   5.650%   $111.2072   $111.21   $111.20   $111.20  
  7 purchase totals = $683.69       $723.6706   $723.68   $723.65   $723.70