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 $182.49   10.415%   $201.4963   $201.50   $201.50   $201.50  
  Purchase #2 $211.99   8.377%   $229.7484   $229.75   $229.75   $229.70  
  Purchase #3 $139.42   10.194%   $153.6325   $153.63   $153.65   $153.60  
  Purchase #4 $192.46   3.333%   $198.8747   $198.87   $198.85   $198.90  
  Purchase #5 $161.80   11.379%   $180.2112   $180.21   $180.20   $180.20  
  Purchase #6 $54.43   13.796%   $61.9392   $61.94   $61.95   $61.90  
  Purchase #7 $38.64   5.584%   $40.7977   $40.80   $40.80   $40.80  
  7 purchase totals = $981.23       $1,066.7000   $1,066.70   $1,066.70   $1,066.60