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 $163.57   3.419%   $169.1625   $169.16   $169.15   $169.20  
  Purchase #2 $13.71   7.236%   $14.7021   $14.70   $14.70   $14.70  
  Purchase #3 $176.31   5.250%   $185.5663   $185.57   $185.55   $185.60  
  Purchase #4 $57.37   5.654%   $60.6137   $60.61   $60.60   $60.60  
  Purchase #5 $56.71   6.705%   $60.5124   $60.51   $60.50   $60.50  
  Purchase #6 $247.41   3.384%   $255.7824   $255.78   $255.80   $255.80  
  Purchase #7 $167.62   7.289%   $179.8378   $179.84   $179.85   $179.80  
  7 purchase totals = $882.70       $926.1772   $926.17   $926.15   $926.20