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 $57.81   6.198%   $61.3931   $61.39   $61.40   $61.40  
  Purchase #2 $238.52   13.646%   $271.0684   $271.07   $271.05   $271.10  
  Purchase #3 $215.79   8.864%   $234.9176   $234.92   $234.90   $234.90  
  Purchase #4 $241.96   4.176%   $252.0642   $252.06   $252.05   $252.10  
  Purchase #5 $250.81   8.863%   $273.0393   $273.04   $273.05   $273.00  
  Purchase #6 $220.33   10.361%   $243.1584   $243.16   $243.15   $243.20  
  Purchase #7 $147.97   7.271%   $158.7289   $158.73   $158.75   $158.70  
  7 purchase totals = $1,373.19       $1,494.3699   $1,494.37   $1,494.35   $1,494.40