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 $60.80   11.688%   $67.9063   $67.91   $67.90   $67.90  
  Purchase #2 $191.54   11.566%   $213.6935   $213.69   $213.70   $213.70  
  Purchase #3 $14.96   3.322%   $15.457   $15.46   $15.45   $15.50  
  Purchase #4 $95.42   5.555%   $100.7206   $100.72   $100.70   $100.70  
  Purchase #5 $224.80   7.254%   $241.107   $241.11   $241.10   $241.10  
  Purchase #6 $176.36   4.784%   $184.7971   $184.80   $184.80   $184.80  
  Purchase #7 $129.78   5.420%   $136.8141   $136.81   $136.80   $136.80  
  7 purchase totals = $893.66       $960.4956   $960.50   $960.45   $960.50