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 $216.53   10.584%   $239.4475   $239.45   $239.45   $239.40  
  Purchase #2 $123.33   8.105%   $133.3259   $133.33   $133.35   $133.30  
  Purchase #3 $106.51   9.256%   $116.3686   $116.37   $116.35   $116.40  
  Purchase #4 $58.46   8.185%   $63.245   $63.25   $63.25   $63.20  
  Purchase #5 $219.74   9.815%   $241.3075   $241.31   $241.30   $241.30  
  Purchase #6 $37.38   4.841%   $39.1896   $39.19   $39.20   $39.20  
  Purchase #7 $211.36   8.498%   $229.3214   $229.32   $229.30   $229.30  
  7 purchase totals = $973.31       $1,062.2055   $1,062.22   $1,062.20   $1,062.10