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 $187.65   11.394%   $209.0308   $209.03   $209.05   $209.00  
  Purchase #2 $167.49   4.766%   $175.4726   $175.47   $175.45   $175.50  
  Purchase #3 $248.27   5.695%   $262.409   $262.41   $262.40   $262.40  
  Purchase #4 $245.82   12.273%   $275.9895   $275.99   $276.00   $276.00  
  Purchase #5 $121.78   11.499%   $135.7835   $135.78   $135.80   $135.80  
  Purchase #6 $166.62   4.493%   $174.1062   $174.11   $174.10   $174.10  
  Purchase #7 $156.39   9.785%   $171.6928   $171.69   $171.70   $171.70  
  7 purchase totals = $1,294.02       $1,404.4844   $1,404.48   $1,404.50   $1,404.50