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 $203.67   8.104%   $220.1754   $220.18   $220.20   $220.20  
  Purchase #2 $53.29   7.163%   $57.1072   $57.11   $57.10   $57.10  
  Purchase #3 $39.83   6.609%   $42.4624   $42.46   $42.45   $42.50  
  Purchase #4 $197.41   8.102%   $213.4042   $213.40   $213.40   $213.40  
  Purchase #5 $232.81   9.457%   $254.8268   $254.83   $254.85   $254.80  
  Purchase #6 $183.39   6.263%   $194.8757   $194.88   $194.90   $194.90  
  Purchase #7 $35.92   8.226%   $38.8748   $38.87   $38.85   $38.90  
  7 purchase totals = $946.32       $1,021.7265   $1,021.73   $1,021.75   $1,021.80