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 $92.61   5.123%   $97.3544   $97.35   $97.35   $97.40  
  Purchase #2 $120.29   11.226%   $133.7938   $133.79   $133.80   $133.80  
  Purchase #3 $49.89   9.599%   $54.6789   $54.68   $54.70   $54.70  
  Purchase #4 $195.36   12.493%   $219.7663   $219.77   $219.75   $219.80  
  Purchase #5 $226.94   10.485%   $250.7347   $250.73   $250.75   $250.70  
  Purchase #6 $195.61   10.765%   $216.6674   $216.67   $216.65   $216.70  
  Purchase #7 $22.57   5.156%   $23.7337   $23.73   $23.75   $23.70  
  7 purchase totals = $903.27       $996.7292   $996.72   $996.75   $996.80