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 $165.49   6.351%   $176.0003   $176.00   $176.00   $176.00  
  Purchase #2 $172.35   10.850%   $191.05   $191.05   $191.05   $191.10  
  Purchase #3 $62.70   8.224%   $67.8564   $67.86   $67.85   $67.90  
  Purchase #4 $239.93   3.440%   $248.1836   $248.18   $248.20   $248.20  
  Purchase #5 $21.90   12.467%   $24.6303   $24.63   $24.65   $24.60  
  Purchase #6 $16.87   10.338%   $18.614   $18.61   $18.60   $18.60  
  Purchase #7 $59.88   8.719%   $65.1009   $65.10   $65.10   $65.10  
  7 purchase totals = $739.12       $791.4355   $791.43   $791.45   $791.50