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 $176.42   4.360%   $184.1119   $184.11   $184.10   $184.10  
  Purchase #2 $163.51   12.115%   $183.3192   $183.32   $183.30   $183.30  
  Purchase #3 $238.80   12.331%   $268.2464   $268.25   $268.25   $268.20  
  Purchase #4 $16.61   11.250%   $18.4786   $18.48   $18.50   $18.50  
  Purchase #5 $226.58   8.522%   $245.8891   $245.89   $245.90   $245.90  
  Purchase #6 $211.85   13.819%   $241.1256   $241.13   $241.15   $241.10  
  Purchase #7 $101.69   4.284%   $106.0464   $106.05   $106.05   $106.00  
  7 purchase totals = $1,135.46       $1,247.2172   $1,247.23   $1,247.25   $1,247.10