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 $26.93   9.366%   $29.4523   $29.45   $29.45   $29.50  
  Purchase #2 $197.54   12.633%   $222.4952   $222.50   $222.50   $222.50  
  Purchase #3 $193.41   6.308%   $205.6103   $205.61   $205.60   $205.60  
  Purchase #4 $94.25   3.359%   $97.4159   $97.42   $97.40   $97.40  
  Purchase #5 $193.81   10.334%   $213.8383   $213.84   $213.85   $213.80  
  Purchase #6 $177.39   9.164%   $193.646   $193.65   $193.65   $193.60  
  Purchase #7 $40.56   13.229%   $45.9257   $45.93   $45.95   $45.90  
  7 purchase totals = $923.89       $1,008.3837   $1,008.40   $1,008.40   $1,008.30