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 $22.75   12.871%   $25.6782   $25.68   $25.70   $25.70  
  Purchase #2 $141.56   4.201%   $147.5069   $147.51   $147.50   $147.50  
  Purchase #3 $162.98   3.707%   $169.0217   $169.02   $169.00   $169.00  
  Purchase #4 $27.69   9.298%   $30.2646   $30.26   $30.25   $30.30  
  Purchase #5 $68.46   12.324%   $76.897   $76.90   $76.90   $76.90  
  Purchase #6 $39.26   4.736%   $41.1194   $41.12   $41.10   $41.10  
  Purchase #7 $192.37   13.752%   $218.8247   $218.82   $218.80   $218.80  
  7 purchase totals = $655.07       $709.3125   $709.31   $709.25   $709.30