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 $79.98   10.107%   $88.0636   $88.06   $88.05   $88.10  
  Purchase #2 $116.69   5.160%   $122.7112   $122.71   $122.70   $122.70  
  Purchase #3 $85.80   3.363%   $88.6855   $88.69   $88.70   $88.70  
  Purchase #4 $248.37   4.441%   $259.4001   $259.40   $259.40   $259.40  
  Purchase #5 $179.36   10.499%   $198.191   $198.19   $198.20   $198.20  
  Purchase #6 $69.28   8.300%   $75.0302   $75.03   $75.05   $75.00  
  Purchase #7 $14.76   4.434%   $15.4145   $15.41   $15.40   $15.40  
  7 purchase totals = $794.24       $847.4961   $847.49   $847.50   $847.50