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 $59.35   7.586%   $63.8523   $63.85   $63.85   $63.90  
  Purchase #2 $168.96   13.645%   $192.0146   $192.01   $192.00   $192.00  
  Purchase #3 $170.41   5.602%   $179.9564   $179.96   $179.95   $180.00  
  Purchase #4 $55.62   3.346%   $57.481   $57.48   $57.50   $57.50  
  Purchase #5 $64.62   10.309%   $71.2817   $71.28   $71.30   $71.30  
  Purchase #6 $16.50   5.366%   $17.3854   $17.39   $17.40   $17.40  
  Purchase #7 $177.30   13.211%   $200.7231   $200.72   $200.70   $200.70  
  7 purchase totals = $712.76       $782.6945   $782.69   $782.70   $782.80