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 $208.43   3.780%   $216.3087   $216.31   $216.30   $216.30  
  Purchase #2 $227.73   8.136%   $246.2581   $246.26   $246.25   $246.30  
  Purchase #3 $53.54   6.856%   $57.2107   $57.21   $57.20   $57.20  
  Purchase #4 $204.63   6.198%   $217.313   $217.31   $217.30   $217.30  
  Purchase #5 $62.28   4.277%   $64.9437   $64.94   $64.95   $64.90  
  Purchase #6 $26.38   11.187%   $29.3311   $29.33   $29.35   $29.30  
  Purchase #7 $190.55   4.668%   $199.4449   $199.44   $199.45   $199.40  
  7 purchase totals = $973.54       $1,030.8102   $1,030.80   $1,030.80   $1,030.70