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 $242.89   5.364%   $255.9186   $255.92   $255.90   $255.90  
  Purchase #2 $144.63   12.844%   $163.2063   $163.21   $163.20   $163.20  
  Purchase #3 $218.67   12.702%   $246.4455   $246.45   $246.45   $246.40  
  Purchase #4 $234.57   5.433%   $247.3142   $247.31   $247.30   $247.30  
  Purchase #5 $99.73   8.417%   $108.1243   $108.12   $108.10   $108.10  
  Purchase #6 $95.27   6.851%   $101.7969   $101.80   $101.80   $101.80  
  Purchase #7 $120.45   10.396%   $132.972   $132.97   $132.95   $133.00  
  7 purchase totals = $1,156.21       $1,255.7778   $1,255.78   $1,255.70   $1,255.70