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 $219.37   6.171%   $232.9073   $232.91   $232.90   $232.90  
  Purchase #2 $28.62   4.190%   $29.8192   $29.82   $29.80   $29.80  
  Purchase #3 $66.83   5.860%   $70.7462   $70.75   $70.75   $70.70  
  Purchase #4 $112.83   9.439%   $123.48   $123.48   $123.50   $123.50  
  Purchase #5 $114.83   3.462%   $118.8054   $118.81   $118.80   $118.80  
  Purchase #6 $50.66   12.276%   $56.879   $56.88   $56.90   $56.90  
  Purchase #7 $155.30   4.546%   $162.3599   $162.36   $162.35   $162.40  
  7 purchase totals = $748.44       $794.9970   $795.01   $795.00   $795.00