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 $228.69   5.705%   $241.7368   $241.74   $241.75   $241.70  
  Purchase #2 $11.62   7.530%   $12.495   $12.50   $12.50   $12.50  
  Purchase #3 $75.76   6.443%   $80.6412   $80.64   $80.65   $80.60  
  Purchase #4 $69.96   7.858%   $75.4575   $75.46   $75.45   $75.50  
  Purchase #5 $238.36   6.830%   $254.64   $254.64   $254.65   $254.60  
  Purchase #6 $107.61   8.385%   $116.6331   $116.63   $116.65   $116.60  
  Purchase #7 $213.27   12.280%   $239.4596   $239.46   $239.45   $239.50  
  7 purchase totals = $945.27       $1,021.0632   $1,021.07   $1,021.10   $1,021.00