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 $126.61   6.437%   $134.7599   $134.76   $134.75   $134.80  
  Purchase #2 $101.50   13.321%   $115.0208   $115.02   $115.00   $115.00  
  Purchase #3 $60.89   12.332%   $68.399   $68.40   $68.40   $68.40  
  Purchase #4 $84.32   9.791%   $92.5758   $92.58   $92.60   $92.60  
  Purchase #5 $78.77   12.359%   $88.5052   $88.51   $88.50   $88.50  
  Purchase #6 $5.38   7.187%   $5.7667   $5.77   $5.75   $5.80  
  Purchase #7 $185.73   9.129%   $202.6853   $202.69   $202.70   $202.70  
  7 purchase totals = $643.20       $707.7127   $707.73   $707.70   $707.80