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 $67.90   4.842%   $71.1877   $71.19   $71.20   $71.20  
  Purchase #2 $240.29   13.178%   $271.9554   $271.96   $271.95   $272.00  
  Purchase #3 $198.86   13.664%   $226.0322   $226.03   $226.05   $226.00  
  Purchase #4 $169.42   3.576%   $175.4785   $175.48   $175.50   $175.50  
  Purchase #5 $76.77   7.834%   $82.7842   $82.78   $82.80   $82.80  
  Purchase #6 $138.64   4.733%   $145.2018   $145.20   $145.20   $145.20  
  Purchase #7 $227.75   10.480%   $251.6182   $251.62   $251.60   $251.60  
  7 purchase totals = $1,119.63       $1,224.2580   $1,224.26   $1,224.30   $1,224.30