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 $198.43   4.121%   $206.6073   $206.61   $206.60   $206.60  
  Purchase #2 $38.58   10.698%   $42.7073   $42.71   $42.70   $42.70  
  Purchase #3 $166.76   6.115%   $176.9574   $176.96   $176.95   $177.00  
  Purchase #4 $184.49   11.538%   $205.7765   $205.78   $205.80   $205.80  
  Purchase #5 $141.81   4.248%   $147.8341   $147.83   $147.85   $147.80  
  Purchase #6 $93.84   11.561%   $104.6888   $104.69   $104.70   $104.70  
  Purchase #7 $69.97   6.374%   $74.4299   $74.43   $74.45   $74.40  
  7 purchase totals = $893.88       $959.0013   $959.01   $959.05   $959.00