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 $63.94   7.422%   $68.6856   $68.69   $68.70   $68.70  
  Purchase #2 $63.42   6.454%   $67.5131   $67.51   $67.50   $67.50  
  Purchase #3 $236.89   6.339%   $251.9065   $251.91   $251.90   $251.90  
  Purchase #4 $211.57   9.844%   $232.397   $232.40   $232.40   $232.40  
  Purchase #5 $57.73   8.195%   $62.461   $62.46   $62.45   $62.50  
  Purchase #6 $243.77   11.512%   $271.8328   $271.83   $271.85   $271.80  
  Purchase #7 $148.71   11.586%   $165.9395   $165.94   $165.95   $165.90  
  7 purchase totals = $1,026.03       $1,120.7355   $1,120.74   $1,120.75   $1,120.70