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 $238.90   6.325%   $254.0104   $254.01   $254.00   $254.00  
  Purchase #2 $191.95   8.213%   $207.7149   $207.71   $207.70   $207.70  
  Purchase #3 $149.57   5.123%   $157.2325   $157.23   $157.25   $157.20  
  Purchase #4 $62.61   3.652%   $64.8965   $64.90   $64.90   $64.90  
  Purchase #5 $35.89   13.604%   $40.7725   $40.77   $40.75   $40.80  
  Purchase #6 $152.55   11.603%   $170.2504   $170.25   $170.25   $170.30  
  Purchase #7 $163.93   6.594%   $174.7395   $174.74   $174.75   $174.70  
  7 purchase totals = $995.40       $1,069.6167   $1,069.61   $1,069.60   $1,069.60