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 $66.75   3.662%   $69.1944   $69.19   $69.20   $69.20  
  Purchase #2 $181.66   12.408%   $204.2004   $204.20   $204.20   $204.20  
  Purchase #3 $62.51   6.437%   $66.5338   $66.53   $66.55   $66.50  
  Purchase #4 $105.35   7.255%   $112.9931   $112.99   $113.00   $113.00  
  Purchase #5 $196.33   9.156%   $214.306   $214.31   $214.30   $214.30  
  Purchase #6 $204.52   5.399%   $215.562   $215.56   $215.55   $215.60  
  Purchase #7 $72.26   12.273%   $81.1285   $81.13   $81.15   $81.10  
  7 purchase totals = $889.38       $963.9182   $963.91   $963.95   $963.90