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 $72.49   12.585%   $81.6129   $81.61   $81.60   $81.60  
  Purchase #2 $187.87   3.225%   $193.9288   $193.93   $193.95   $193.90  
  Purchase #3 $216.69   8.585%   $235.2928   $235.29   $235.30   $235.30  
  Purchase #4 $127.49   4.111%   $132.7311   $132.73   $132.75   $132.70  
  Purchase #5 $171.80   4.574%   $179.6581   $179.66   $179.65   $179.70  
  Purchase #6 $179.67   9.479%   $196.7009   $196.70   $196.70   $196.70  
  Purchase #7 $59.66   4.635%   $62.4252   $62.43   $62.45   $62.40  
  7 purchase totals = $1,015.67       $1,082.3498   $1,082.35   $1,082.40   $1,082.30