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 $46.71   6.674%   $49.8274   $49.83   $49.85   $49.80  
  Purchase #2 $197.34   3.368%   $203.9864   $203.99   $204.00   $204.00  
  Purchase #3 $47.97   3.798%   $49.7919   $49.79   $49.80   $49.80  
  Purchase #4 $172.56   10.209%   $190.1767   $190.18   $190.20   $190.20  
  Purchase #5 $218.37   5.469%   $230.3127   $230.31   $230.30   $230.30  
  Purchase #6 $62.78   13.749%   $71.4116   $71.41   $71.40   $71.40  
  Purchase #7 $217.68   4.705%   $227.9218   $227.92   $227.90   $227.90  
  7 purchase totals = $963.41       $1,023.4285   $1,023.43   $1,023.45   $1,023.40