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 $231.88   6.406%   $246.7342   $246.73   $246.75   $246.70  
  Purchase #2 $102.64   6.808%   $109.6277   $109.63   $109.65   $109.60  
  Purchase #3 $212.67   5.794%   $224.9921   $224.99   $225.00   $225.00  
  Purchase #4 $105.54   9.602%   $115.674   $115.67   $115.65   $115.70  
  Purchase #5 $24.75   10.582%   $27.369   $27.37   $27.35   $27.40  
  Purchase #6 $141.76   8.437%   $153.7203   $153.72   $153.70   $153.70  
  Purchase #7 $173.50   7.333%   $186.2228   $186.22   $186.20   $186.20  
  7 purchase totals = $992.74       $1,064.3401   $1,064.33   $1,064.30   $1,064.30