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 $246.34   12.852%   $277.9996   $278.00   $278.00   $278.00  
  Purchase #2 $194.61   10.529%   $215.1005   $215.10   $215.10   $215.10  
  Purchase #3 $182.44   8.241%   $197.4749   $197.47   $197.45   $197.50  
  Purchase #4 $71.93   4.336%   $75.0489   $75.05   $75.05   $75.00  
  Purchase #5 $39.26   5.679%   $41.4896   $41.49   $41.50   $41.50  
  Purchase #6 $212.88   3.691%   $220.7374   $220.74   $220.75   $220.70  
  Purchase #7 $67.67   12.583%   $76.1849   $76.18   $76.20   $76.20  
  7 purchase totals = $1,015.13       $1,104.0358   $1,104.03   $1,104.05   $1,104.00