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 $248.49   11.524%   $277.126   $277.13   $277.15   $277.10  
  Purchase #2 $101.98   7.801%   $109.9355   $109.94   $109.95   $109.90  
  Purchase #3 $44.68   13.359%   $50.6488   $50.65   $50.65   $50.60  
  Purchase #4 $119.29   4.592%   $124.7678   $124.77   $124.75   $124.80  
  Purchase #5 $86.74   11.240%   $96.4896   $96.49   $96.50   $96.50  
  Purchase #6 $163.68   8.321%   $177.2998   $177.30   $177.30   $177.30  
  Purchase #7 $198.50   8.222%   $214.8207   $214.82   $214.80   $214.80  
  7 purchase totals = $963.36       $1,051.0882   $1,051.10   $1,051.10   $1,051.00