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 $163.41   8.559%   $177.3963   $177.40   $177.40   $177.40  
  Purchase #2 $201.75   7.678%   $217.2404   $217.24   $217.25   $217.20  
  Purchase #3 $116.99   10.198%   $128.9206   $128.92   $128.90   $128.90  
  Purchase #4 $78.81   3.629%   $81.67   $81.67   $81.65   $81.70  
  Purchase #5 $33.40   9.455%   $36.558   $36.56   $36.55   $36.60  
  Purchase #6 $190.44   3.787%   $197.652   $197.65   $197.65   $197.70  
  Purchase #7 $148.83   3.166%   $153.542   $153.54   $153.55   $153.50  
  7 purchase totals = $933.63       $992.9793   $992.98   $992.95   $993.00