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 $53.32   6.332%   $56.6962   $56.70   $56.70   $56.70  
  Purchase #2 $217.88   10.109%   $239.9055   $239.91   $239.90   $239.90  
  Purchase #3 $250.99   11.587%   $280.0722   $280.07   $280.05   $280.10  
  Purchase #4 $129.86   12.251%   $145.7691   $145.77   $145.75   $145.80  
  Purchase #5 $29.35   9.403%   $32.1098   $32.11   $32.10   $32.10  
  Purchase #6 $140.99   3.816%   $146.3702   $146.37   $146.35   $146.40  
  Purchase #7 $144.85   11.817%   $161.9669   $161.97   $161.95   $162.00  
  7 purchase totals = $967.24       $1,062.8899   $1,062.90   $1,062.80   $1,063.00