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 $227.69   11.482%   $253.8334   $253.83   $253.85   $253.80  
  Purchase #2 $37.73   11.554%   $42.0893   $42.09   $42.10   $42.10  
  Purchase #3 $248.43   7.749%   $267.6808   $267.68   $267.70   $267.70  
  Purchase #4 $108.29   4.821%   $113.5107   $113.51   $113.50   $113.50  
  Purchase #5 $203.66   3.348%   $210.4785   $210.48   $210.50   $210.50  
  Purchase #6 $83.42   4.315%   $87.0196   $87.02   $87.00   $87.00  
  Purchase #7 $136.67   6.370%   $145.3759   $145.38   $145.40   $145.40  
  7 purchase totals = $1,045.89       $1,119.9882   $1,119.99   $1,120.05   $1,120.00