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 $249.97   13.196%   $282.956   $282.96   $282.95   $283.00  
  Purchase #2 $95.42   7.659%   $102.7282   $102.73   $102.75   $102.70  
  Purchase #3 $142.74   11.404%   $159.0181   $159.02   $159.00   $159.00  
  Purchase #4 $239.54   5.396%   $252.4656   $252.47   $252.45   $252.50  
  Purchase #5 $190.64   7.475%   $204.8903   $204.89   $204.90   $204.90  
  Purchase #6 $202.78   8.662%   $220.3448   $220.34   $220.35   $220.30  
  Purchase #7 $166.25   3.626%   $172.2782   $172.28   $172.30   $172.30  
  7 purchase totals = $1,287.34       $1,394.6812   $1,394.69   $1,394.70   $1,394.70