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 $213.62   13.253%   $241.9311   $241.93   $241.95   $241.90  
  Purchase #2 $11.61   4.191%   $12.0966   $12.10   $12.10   $12.10  
  Purchase #3 $38.87   12.226%   $43.6222   $43.62   $43.60   $43.60  
  Purchase #4 $209.45   5.864%   $221.7321   $221.73   $221.75   $221.70  
  Purchase #5 $139.81   10.696%   $154.7641   $154.76   $154.75   $154.80  
  Purchase #6 $146.47   9.717%   $160.7025   $160.70   $160.70   $160.70  
  Purchase #7 $216.42   11.119%   $240.4837   $240.48   $240.50   $240.50  
  7 purchase totals = $976.25       $1,075.3323   $1,075.32   $1,075.35   $1,075.30