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 $209.92   12.796%   $236.7814   $236.78   $236.80   $236.80  
  Purchase #2 $94.41   4.495%   $98.6537   $98.65   $98.65   $98.70  
  Purchase #3 $62.93   13.567%   $71.4677   $71.47   $71.45   $71.50  
  Purchase #4 $87.26   8.854%   $94.986   $94.99   $95.00   $95.00  
  Purchase #5 $168.99   3.751%   $175.3288   $175.33   $175.35   $175.30  
  Purchase #6 $245.51   4.685%   $257.0121   $257.01   $257.00   $257.00  
  Purchase #7 $33.31   5.862%   $35.2626   $35.26   $35.25   $35.30  
  7 purchase totals = $902.33       $969.4923   $969.49   $969.50   $969.60