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 $227.98   9.207%   $248.9701   $248.97   $248.95   $249.00  
  Purchase #2 $56.28   7.587%   $60.55   $60.55   $60.55   $60.60  
  Purchase #3 $158.86   8.519%   $172.3933   $172.39   $172.40   $172.40  
  Purchase #4 $234.27   8.747%   $254.7616   $254.76   $254.75   $254.80  
  Purchase #5 $5.91   8.136%   $6.3908   $6.39   $6.40   $6.40  
  Purchase #6 $201.75   12.542%   $227.0535   $227.05   $227.05   $227.10  
  Purchase #7 $39.98   9.167%   $43.645   $43.65   $43.65   $43.60  
  7 purchase totals = $925.03       $1,013.7643   $1,013.76   $1,013.75   $1,013.90