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 $162.51   13.614%   $184.6341   $184.63   $184.65   $184.60  
  Purchase #2 $161.50   4.437%   $168.6658   $168.67   $168.65   $168.70  
  Purchase #3 $26.75   12.739%   $30.1577   $30.16   $30.15   $30.20  
  Purchase #4 $213.63   11.370%   $237.9197   $237.92   $237.90   $237.90  
  Purchase #5 $247.29   12.825%   $279.0049   $279.00   $279.00   $279.00  
  Purchase #6 $78.36   11.358%   $87.2601   $87.26   $87.25   $87.30  
  Purchase #7 $83.54   6.303%   $88.8055   $88.81   $88.80   $88.80  
  7 purchase totals = $973.58       $1,076.4478   $1,076.45   $1,076.40   $1,076.50