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 $64.36   4.447%   $67.2221   $67.22   $67.20   $67.20  
  Purchase #2 $88.29   12.296%   $99.1461   $99.15   $99.15   $99.10  
  Purchase #3 $16.28   10.183%   $17.9378   $17.94   $17.95   $17.90  
  Purchase #4 $216.29   12.114%   $242.4914   $242.49   $242.50   $242.50  
  Purchase #5 $91.35   8.842%   $99.4272   $99.43   $99.45   $99.40  
  Purchase #6 $193.35   13.442%   $219.3401   $219.34   $219.35   $219.30  
  Purchase #7 $95.90   12.380%   $107.7724   $107.77   $107.75   $107.80  
  7 purchase totals = $765.82       $853.3371   $853.34   $853.35   $853.20