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 $234.85   11.454%   $261.7497   $261.75   $261.75   $261.70  
  Purchase #2 $58.98   7.517%   $63.4135   $63.41   $63.40   $63.40  
  Purchase #3 $244.85   13.422%   $277.7138   $277.71   $277.70   $277.70  
  Purchase #4 $53.57   12.437%   $60.2325   $60.23   $60.25   $60.20  
  Purchase #5 $198.58   7.703%   $213.8766   $213.88   $213.90   $213.90  
  Purchase #6 $184.83   8.767%   $201.034   $201.03   $201.05   $201.00  
  Purchase #7 $27.69   4.634%   $28.9732   $28.97   $28.95   $29.00  
  7 purchase totals = $1,003.35       $1,106.9933   $1,106.98   $1,107.00   $1,106.90