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 $194.89   12.367%   $218.992   $218.99   $219.00   $219.00  
  Purchase #2 $122.36   12.110%   $137.1778   $137.18   $137.20   $137.20  
  Purchase #3 $173.88   11.187%   $193.332   $193.33   $193.35   $193.30  
  Purchase #4 $163.88   11.122%   $182.1067   $182.11   $182.10   $182.10  
  Purchase #5 $203.69   6.726%   $217.3902   $217.39   $217.40   $217.40  
  Purchase #6 $175.49   5.364%   $184.9033   $184.90   $184.90   $184.90  
  Purchase #7 $136.71   7.746%   $147.2996   $147.30   $147.30   $147.30  
  7 purchase totals = $1,170.90       $1,281.2016   $1,281.20   $1,281.25   $1,281.20