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 $228.77   12.759%   $257.9588   $257.96   $257.95   $258.00  
  Purchase #2 $248.61   11.659%   $277.5954   $277.60   $277.60   $277.60  
  Purchase #3 $112.85   9.845%   $123.9601   $123.96   $123.95   $124.00  
  Purchase #4 $215.43   11.403%   $239.9955   $240.00   $240.00   $240.00  
  Purchase #5 $122.44   6.570%   $130.4843   $130.48   $130.50   $130.50  
  Purchase #6 $84.40   5.787%   $89.2842   $89.28   $89.30   $89.30  
  Purchase #7 $43.82   12.474%   $49.2861   $49.29   $49.30   $49.30  
  7 purchase totals = $1,056.32       $1,168.5644   $1,168.57   $1,168.60   $1,168.70