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 $54.89   7.480%   $58.9958   $59.00   $59.00   $59.00  
  Purchase #2 $249.70   3.789%   $259.1611   $259.16   $259.15   $259.20  
  Purchase #3 $212.63   5.701%   $224.752   $224.75   $224.75   $224.80  
  Purchase #4 $188.65   9.654%   $206.8623   $206.86   $206.85   $206.90  
  Purchase #5 $197.67   5.445%   $208.4331   $208.43   $208.45   $208.40  
  Purchase #6 $5.89   9.581%   $6.4543   $6.45   $6.45   $6.50  
  Purchase #7 $136.28   13.277%   $154.3739   $154.37   $154.35   $154.40  
  7 purchase totals = $1,045.71       $1,119.0325   $1,119.02   $1,119.00   $1,119.20