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 $245.80   11.623%   $274.3693   $274.37   $274.35   $274.40  
  Purchase #2 $49.44   13.605%   $56.1663   $56.17   $56.15   $56.20  
  Purchase #3 $148.49   6.569%   $158.2443   $158.24   $158.25   $158.20  
  Purchase #4 $12.48   10.868%   $13.8363   $13.84   $13.85   $13.80  
  Purchase #5 $119.44   11.280%   $132.9128   $132.91   $132.90   $132.90  
  Purchase #6 $177.94   8.818%   $193.6307   $193.63   $193.65   $193.60  
  Purchase #7 $202.86   4.797%   $212.5912   $212.59   $212.60   $212.60  
  7 purchase totals = $956.45       $1,041.7509   $1,041.75   $1,041.75   $1,041.70