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 $76.69   10.225%   $84.5316   $84.53   $84.55   $84.50  
  Purchase #2 $245.61   3.386%   $253.9264   $253.93   $253.95   $253.90  
  Purchase #3 $127.93   11.258%   $142.3324   $142.33   $142.35   $142.30  
  Purchase #4 $247.39   13.132%   $279.8773   $279.88   $279.90   $279.90  
  Purchase #5 $217.37   4.233%   $226.5713   $226.57   $226.55   $226.60  
  Purchase #6 $152.50   10.347%   $168.2792   $168.28   $168.30   $168.30  
  Purchase #7 $214.63   11.256%   $238.7888   $238.79   $238.80   $238.80  
  7 purchase totals = $1,282.12       $1,394.3070   $1,394.31   $1,394.40   $1,394.30