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 $233.92   11.657%   $261.1881   $261.19   $261.20   $261.20  
  Purchase #2 $202.91   8.839%   $220.8452   $220.85   $220.85   $220.80  
  Purchase #3 $50.71   10.427%   $55.9975   $56.00   $56.00   $56.00  
  Purchase #4 $49.99   9.822%   $54.9   $54.90   $54.90   $54.90  
  Purchase #5 $152.33   10.840%   $168.8426   $168.84   $168.85   $168.80  
  Purchase #6 $146.28   12.585%   $164.6893   $164.69   $164.70   $164.70  
  Purchase #7 $216.59   5.822%   $229.1999   $229.20   $229.20   $229.20  
  7 purchase totals = $1,052.73       $1,155.6626   $1,155.67   $1,155.70   $1,155.60