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 $247.47   10.207%   $272.7293   $272.73   $272.75   $272.70  
  Purchase #2 $178.29   10.176%   $196.4328   $196.43   $196.45   $196.40  
  Purchase #3 $146.49   5.501%   $154.5484   $154.55   $154.55   $154.50  
  Purchase #4 $224.74   8.342%   $243.4878   $243.49   $243.50   $243.50  
  Purchase #5 $227.76   5.646%   $240.6193   $240.62   $240.60   $240.60  
  Purchase #6 $38.54   6.757%   $41.1441   $41.14   $41.15   $41.10  
  Purchase #7 $207.37   5.861%   $219.524   $219.52   $219.50   $219.50  
  7 purchase totals = $1,270.66       $1,368.4857   $1,368.48   $1,368.50   $1,368.30