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 $35.41   5.447%   $37.3388   $37.34   $37.35   $37.30  
  Purchase #2 $99.45   4.483%   $103.9083   $103.91   $103.90   $103.90  
  Purchase #3 $148.56   9.598%   $162.8188   $162.82   $162.80   $162.80  
  Purchase #4 $12.56   3.816%   $13.0393   $13.04   $13.05   $13.00  
  Purchase #5 $129.51   4.414%   $135.2266   $135.23   $135.25   $135.20  
  Purchase #6 $56.81   5.629%   $60.0078   $60.01   $60.00   $60.00  
  Purchase #7 $198.61   8.663%   $215.8156   $215.82   $215.80   $215.80  
  7 purchase totals = $680.91       $728.1552   $728.17   $728.15   $728.00