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 $236.62   13.831%   $269.3469   $269.35   $269.35   $269.30  
  Purchase #2 $170.31   13.551%   $193.3887   $193.39   $193.40   $193.40  
  Purchase #3 $170.33   8.565%   $184.9188   $184.92   $184.90   $184.90  
  Purchase #4 $118.62   9.151%   $129.4749   $129.47   $129.45   $129.50  
  Purchase #5 $186.63   5.731%   $197.3258   $197.33   $197.35   $197.30  
  Purchase #6 $212.84   3.673%   $220.6576   $220.66   $220.65   $220.70  
  Purchase #7 $36.57   4.394%   $38.1769   $38.18   $38.20   $38.20  
  7 purchase totals = $1,131.92       $1,233.2896   $1,233.30   $1,233.30   $1,233.30