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 $139.82   5.349%   $147.299   $147.30   $147.30   $147.30  
  Purchase #2 $174.81   8.293%   $189.307   $189.31   $189.30   $189.30  
  Purchase #3 $162.45   8.172%   $175.7254   $175.73   $175.75   $175.70  
  Purchase #4 $21.76   12.874%   $24.5614   $24.56   $24.55   $24.60  
  Purchase #5 $230.63   6.845%   $246.4166   $246.42   $246.40   $246.40  
  Purchase #6 $13.85   10.227%   $15.2664   $15.27   $15.25   $15.30  
  Purchase #7 $225.91   5.162%   $237.5715   $237.57   $237.55   $237.60  
  7 purchase totals = $969.23       $1,036.1473   $1,036.16   $1,036.10   $1,036.20