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 $51.67   13.425%   $58.6067   $58.61   $58.60   $58.60  
  Purchase #2 $237.34   6.106%   $251.832   $251.83   $251.85   $251.80  
  Purchase #3 $201.72   5.673%   $213.1636   $213.16   $213.15   $213.20  
  Purchase #4 $234.58   11.676%   $261.9696   $261.97   $261.95   $262.00  
  Purchase #5 $69.61   8.689%   $75.6584   $75.66   $75.65   $75.70  
  Purchase #6 $215.65   12.220%   $242.0024   $242.00   $242.00   $242.00  
  Purchase #7 $100.81   7.154%   $108.0219   $108.02   $108.00   $108.00  
  7 purchase totals = $1,111.38       $1,211.2546   $1,211.25   $1,211.20   $1,211.30