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 $203.97   8.630%   $221.5726   $221.57   $221.55   $221.60  
  Purchase #2 $145.59   12.192%   $163.3403   $163.34   $163.35   $163.30  
  Purchase #3 $162.95   6.227%   $173.0969   $173.10   $173.10   $173.10  
  Purchase #4 $237.66   5.305%   $250.2679   $250.27   $250.25   $250.30  
  Purchase #5 $214.79   9.126%   $234.3917   $234.39   $234.40   $234.40  
  Purchase #6 $199.38   6.321%   $211.9828   $211.98   $212.00   $212.00  
  Purchase #7 $16.33   12.314%   $18.3409   $18.34   $18.35   $18.30  
  7 purchase totals = $1,180.67       $1,272.9931   $1,272.99   $1,273.00   $1,273.00