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 $224.93   11.400%   $250.572   $250.57   $250.55   $250.60  
  Purchase #2 $116.82   8.296%   $126.5114   $126.51   $126.50   $126.50  
  Purchase #3 $60.27   4.545%   $63.0093   $63.01   $63.00   $63.00  
  Purchase #4 $53.55   13.289%   $60.6663   $60.67   $60.65   $60.70  
  Purchase #5 $186.72   4.134%   $194.439   $194.44   $194.45   $194.40  
  Purchase #6 $203.76   8.701%   $221.4892   $221.49   $221.50   $221.50  
  Purchase #7 $171.32   13.839%   $195.029   $195.03   $195.05   $195.00  
  7 purchase totals = $1,017.37       $1,111.7162   $1,111.72   $1,111.70   $1,111.70