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 $60.41   9.391%   $66.0831   $66.08   $66.10   $66.10  
  Purchase #2 $77.45   3.671%   $80.2932   $80.29   $80.30   $80.30  
  Purchase #3 $218.63   4.455%   $228.37   $228.37   $228.35   $228.40  
  Purchase #4 $43.88   6.562%   $46.7594   $46.76   $46.75   $46.80  
  Purchase #5 $236.54   6.738%   $252.4781   $252.48   $252.50   $252.50  
  Purchase #6 $233.40   11.447%   $260.1173   $260.12   $260.10   $260.10  
  Purchase #7 $209.46   8.392%   $227.0379   $227.04   $227.05   $227.00  
  7 purchase totals = $1,079.77       $1,161.1390   $1,161.14   $1,161.15   $1,161.20