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 $120.76   11.371%   $134.4916   $134.49   $134.50   $134.50  
  Purchase #2 $71.66   6.175%   $76.085   $76.09   $76.10   $76.10  
  Purchase #3 $131.27   11.787%   $146.7428   $146.74   $146.75   $146.70  
  Purchase #4 $242.64   4.561%   $253.7068   $253.71   $253.70   $253.70  
  Purchase #5 $226.26   11.206%   $251.6147   $251.61   $251.60   $251.60  
  Purchase #6 $220.43   11.656%   $246.1233   $246.12   $246.10   $246.10  
  Purchase #7 $242.96   5.439%   $256.1746   $256.17   $256.15   $256.20  
  7 purchase totals = $1,255.98       $1,364.9388   $1,364.93   $1,364.90   $1,364.90