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 $14.65   11.716%   $16.3664   $16.37   $16.35   $16.40  
  Purchase #2 $232.50   12.257%   $260.9975   $261.00   $261.00   $261.00  
  Purchase #3 $140.47   10.141%   $154.7151   $154.72   $154.70   $154.70  
  Purchase #4 $72.34   12.396%   $81.3073   $81.31   $81.30   $81.30  
  Purchase #5 $213.88   4.518%   $223.5431   $223.54   $223.55   $223.50  
  Purchase #6 $154.80   12.605%   $174.3125   $174.31   $174.30   $174.30  
  Purchase #7 $92.45   11.802%   $103.3609   $103.36   $103.35   $103.40  
  7 purchase totals = $921.09       $1,014.6028   $1,014.61   $1,014.55   $1,014.60