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 $102.98   8.496%   $111.7292   $111.73   $111.75   $111.70  
  Purchase #2 $232.84   12.209%   $261.2674   $261.27   $261.25   $261.30  
  Purchase #3 $147.90   6.391%   $157.3523   $157.35   $157.35   $157.40  
  Purchase #4 $73.93   11.493%   $82.4268   $82.43   $82.45   $82.40  
  Purchase #5 $65.37   6.280%   $69.4752   $69.48   $69.50   $69.50  
  Purchase #6 $231.57   6.522%   $246.673   $246.67   $246.65   $246.70  
  Purchase #7 $132.96   4.791%   $139.3301   $139.33   $139.35   $139.30  
  7 purchase totals = $987.55       $1,068.2540   $1,068.26   $1,068.30   $1,068.30