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 $227.77   9.563%   $249.5516   $249.55   $249.55   $249.60  
  Purchase #2 $46.96   11.202%   $52.2205   $52.22   $52.20   $52.20  
  Purchase #3 $84.35   8.739%   $91.7213   $91.72   $91.70   $91.70  
  Purchase #4 $136.98   12.157%   $153.6327   $153.63   $153.65   $153.60  
  Purchase #5 $156.65   3.399%   $161.9745   $161.97   $161.95   $162.00  
  Purchase #6 $230.96   3.771%   $239.6695   $239.67   $239.65   $239.70  
  Purchase #7 $76.93   9.280%   $84.0691   $84.07   $84.05   $84.10  
  7 purchase totals = $960.60       $1,032.8392   $1,032.83   $1,032.75   $1,032.90