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 $56.82   7.690%   $61.1895   $61.19   $61.20   $61.20  
  Purchase #2 $164.69   10.160%   $181.4225   $181.42   $181.40   $181.40  
  Purchase #3 $47.60   4.574%   $49.7772   $49.78   $49.80   $49.80  
  Purchase #4 $139.47   6.305%   $148.2636   $148.26   $148.25   $148.30  
  Purchase #5 $156.29   3.355%   $161.5335   $161.53   $161.55   $161.50  
  Purchase #6 $5.50   4.534%   $5.7494   $5.75   $5.75   $5.70  
  Purchase #7 $113.77   4.354%   $118.7235   $118.72   $118.70   $118.70  
  7 purchase totals = $684.14       $726.6592   $726.65   $726.65   $726.60