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 $68.33   11.470%   $76.1675   $76.17   $76.15   $76.20  
  Purchase #2 $29.44   8.694%   $31.9995   $32.00   $32.00   $32.00  
  Purchase #3 $66.93   8.653%   $72.7215   $72.72   $72.70   $72.70  
  Purchase #4 $136.62   10.551%   $151.0348   $151.03   $151.05   $151.00  
  Purchase #5 $218.97   10.278%   $241.4757   $241.48   $241.50   $241.50  
  Purchase #6 $199.71   13.598%   $226.8666   $226.87   $226.85   $226.90  
  Purchase #7 $235.74   12.342%   $264.835   $264.84   $264.85   $264.80  
  7 purchase totals = $955.74       $1,065.1006   $1,065.11   $1,065.10   $1,065.10