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 $154.63   9.114%   $168.723   $168.72   $168.70   $168.70  
  Purchase #2 $6.96   11.672%   $7.7724   $7.77   $7.75   $7.80  
  Purchase #3 $55.65   9.407%   $60.885   $60.89   $60.90   $60.90  
  Purchase #4 $184.75   6.108%   $196.0345   $196.03   $196.05   $196.00  
  Purchase #5 $106.25   12.154%   $119.1636   $119.16   $119.15   $119.20  
  Purchase #6 $60.76   13.262%   $68.818   $68.82   $68.80   $68.80  
  Purchase #7 $226.27   6.632%   $241.2762   $241.28   $241.30   $241.30  
  7 purchase totals = $795.27       $862.6727   $862.67   $862.65   $862.70