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 $246.36   10.209%   $271.5109   $271.51   $271.50   $271.50  
  Purchase #2 $204.81   13.675%   $232.8178   $232.82   $232.80   $232.80  
  Purchase #3 $240.52   9.847%   $264.204   $264.20   $264.20   $264.20  
  Purchase #4 $218.59   9.685%   $239.7604   $239.76   $239.75   $239.80  
  Purchase #5 $137.42   5.465%   $144.93   $144.93   $144.95   $144.90  
  Purchase #6 $51.64   3.344%   $53.3668   $53.37   $53.35   $53.40  
  Purchase #7 $219.87   7.668%   $236.7296   $236.73   $236.75   $236.70  
  7 purchase totals = $1,319.21       $1,443.3195   $1,443.32   $1,443.30   $1,443.30