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 $235.26   13.332%   $266.6249   $266.62   $266.60   $266.60  
  Purchase #2 $208.97   11.299%   $232.5815   $232.58   $232.60   $232.60  
  Purchase #3 $64.32   7.430%   $69.099   $69.10   $69.10   $69.10  
  Purchase #4 $155.32   3.322%   $160.4797   $160.48   $160.50   $160.50  
  Purchase #5 $171.60   3.548%   $177.6884   $177.69   $177.70   $177.70  
  Purchase #6 $216.93   5.621%   $229.1236   $229.12   $229.10   $229.10  
  Purchase #7 $124.74   6.370%   $132.6859   $132.69   $132.70   $132.70  
  7 purchase totals = $1,177.14       $1,268.2830   $1,268.28   $1,268.30   $1,268.30