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 $168.97   8.828%   $183.8867   $183.89   $183.90   $183.90  
  Purchase #2 $186.30   9.266%   $203.5626   $203.56   $203.55   $203.60  
  Purchase #3 $154.36   13.665%   $175.4533   $175.45   $175.45   $175.50  
  Purchase #4 $218.48   10.552%   $241.534   $241.53   $241.55   $241.50  
  Purchase #5 $50.87   7.772%   $54.8236   $54.82   $54.80   $54.80  
  Purchase #6 $48.46   7.789%   $52.2345   $52.23   $52.25   $52.20  
  Purchase #7 $119.47   11.797%   $133.5639   $133.56   $133.55   $133.60  
  7 purchase totals = $946.91       $1,045.0586   $1,045.04   $1,045.05   $1,045.10