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 $187.69   10.579%   $207.5457   $207.55   $207.55   $207.50  
  Purchase #2 $61.71   9.813%   $67.7656   $67.77   $67.75   $67.80  
  Purchase #3 $169.55   4.763%   $177.6257   $177.63   $177.65   $177.60  
  Purchase #4 $157.47   10.741%   $174.3839   $174.38   $174.40   $174.40  
  Purchase #5 $106.87   10.160%   $117.728   $117.73   $117.75   $117.70  
  Purchase #6 $197.27   11.313%   $219.5872   $219.59   $219.60   $219.60  
  Purchase #7 $24.96   5.642%   $26.3682   $26.37   $26.35   $26.40  
  7 purchase totals = $905.52       $991.0043   $991.02   $991.05   $991.00