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 $85.78   8.303%   $92.9023   $92.90   $92.90   $92.90  
  Purchase #2 $229.93   6.547%   $244.9835   $244.98   $245.00   $245.00  
  Purchase #3 $151.54   7.741%   $163.2707   $163.27   $163.25   $163.30  
  Purchase #4 $197.99   3.825%   $205.5631   $205.56   $205.55   $205.60  
  Purchase #5 $239.45   5.312%   $252.1696   $252.17   $252.15   $252.20  
  Purchase #6 $168.51   8.283%   $182.4677   $182.47   $182.45   $182.50  
  Purchase #7 $10.46   13.146%   $11.8351   $11.84   $11.85   $11.80  
  7 purchase totals = $1,083.66       $1,153.1920   $1,153.19   $1,153.15   $1,153.30