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 $146.69   12.664%   $165.2668   $165.27   $165.25   $165.30  
  Purchase #2 $129.38   11.252%   $143.9378   $143.94   $143.95   $143.90  
  Purchase #3 $231.29   10.654%   $255.9316   $255.93   $255.95   $255.90  
  Purchase #4 $125.96   6.110%   $133.6562   $133.66   $133.65   $133.70  
  Purchase #5 $238.73   11.561%   $266.3296   $266.33   $266.35   $266.30  
  Purchase #6 $236.90   13.666%   $269.2748   $269.27   $269.25   $269.30  
  Purchase #7 $16.36   3.577%   $16.9452   $16.95   $16.95   $16.90  
  7 purchase totals = $1,125.31       $1,251.3420   $1,251.35   $1,251.35   $1,251.30