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 $147.84   11.836%   $165.3383   $165.34   $165.35   $165.30  
  Purchase #2 $236.83   9.515%   $259.3644   $259.36   $259.35   $259.40  
  Purchase #3 $73.60   10.619%   $81.4156   $81.42   $81.40   $81.40  
  Purchase #4 $204.49   13.769%   $232.6462   $232.65   $232.65   $232.60  
  Purchase #5 $103.57   6.695%   $110.504   $110.50   $110.50   $110.50  
  Purchase #6 $163.61   13.428%   $185.5796   $185.58   $185.60   $185.60  
  Purchase #7 $158.75   8.161%   $171.7056   $171.71   $171.70   $171.70  
  7 purchase totals = $1,088.69       $1,206.5537   $1,206.56   $1,206.55   $1,206.50