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 $197.53   8.658%   $214.6321   $214.63   $214.65   $214.60  
  Purchase #2 $187.80   8.805%   $204.3358   $204.34   $204.35   $204.30  
  Purchase #3 $165.98   13.563%   $188.4919   $188.49   $188.50   $188.50  
  Purchase #4 $110.68   4.293%   $115.4315   $115.43   $115.45   $115.40  
  Purchase #5 $134.72   3.715%   $139.7248   $139.72   $139.70   $139.70  
  Purchase #6 $66.91   3.477%   $69.2365   $69.24   $69.25   $69.20  
  Purchase #7 $121.68   4.649%   $127.3369   $127.34   $127.35   $127.30  
  7 purchase totals = $985.30       $1,059.1895   $1,059.19   $1,059.25   $1,059.00