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 $164.80   11.182%   $183.2279   $183.23   $183.25   $183.20  
  Purchase #2 $181.82   4.741%   $190.4401   $190.44   $190.45   $190.40  
  Purchase #3 $146.28   12.617%   $164.7361   $164.74   $164.75   $164.70  
  Purchase #4 $185.29   12.161%   $207.8231   $207.82   $207.80   $207.80  
  Purchase #5 $237.94   6.262%   $252.8398   $252.84   $252.85   $252.80  
  Purchase #6 $62.81   4.115%   $65.3946   $65.39   $65.40   $65.40  
  Purchase #7 $10.95   11.773%   $12.2391   $12.24   $12.25   $12.20  
  7 purchase totals = $989.89       $1,076.7007   $1,076.70   $1,076.75   $1,076.50