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 $236.52   9.716%   $259.5003   $259.50   $259.50   $259.50  
  Purchase #2 $146.66   6.712%   $156.5038   $156.50   $156.50   $156.50  
  Purchase #3 $231.68   6.449%   $246.621   $246.62   $246.60   $246.60  
  Purchase #4 $215.40   12.262%   $241.8123   $241.81   $241.80   $241.80  
  Purchase #5 $184.56   9.524%   $202.1375   $202.14   $202.15   $202.10  
  Purchase #6 $86.48   8.597%   $93.9147   $93.91   $93.90   $93.90  
  Purchase #7 $160.84   9.543%   $176.189   $176.19   $176.20   $176.20  
  7 purchase totals = $1,262.14       $1,376.6786   $1,376.67   $1,376.65   $1,376.60