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 $161.84   10.573%   $178.9513   $178.95   $178.95   $179.00  
  Purchase #2 $234.77   9.329%   $256.6717   $256.67   $256.65   $256.70  
  Purchase #3 $227.94   9.619%   $249.8655   $249.87   $249.85   $249.90  
  Purchase #4 $191.48   9.367%   $209.4159   $209.42   $209.40   $209.40  
  Purchase #5 $184.77   11.859%   $206.6819   $206.68   $206.70   $206.70  
  Purchase #6 $149.87   4.269%   $156.268   $156.27   $156.25   $156.30  
  Purchase #7 $80.38   7.860%   $86.6979   $86.70   $86.70   $86.70  
  7 purchase totals = $1,231.05       $1,344.5522   $1,344.56   $1,344.50   $1,344.70