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 $192.82   6.393%   $205.147   $205.15   $205.15   $205.10  
  Purchase #2 $80.99   11.741%   $90.499   $90.50   $90.50   $90.50  
  Purchase #3 $212.51   8.217%   $229.9719   $229.97   $229.95   $230.00  
  Purchase #4 $156.98   11.130%   $174.4519   $174.45   $174.45   $174.50  
  Purchase #5 $77.44   12.321%   $86.9814   $86.98   $87.00   $87.00  
  Purchase #6 $51.59   7.546%   $55.483   $55.48   $55.50   $55.50  
  Purchase #7 $108.29   10.417%   $119.5706   $119.57   $119.55   $119.60  
  7 purchase totals = $880.62       $962.1048   $962.10   $962.10   $962.20