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 $69.57   3.523%   $72.021   $72.02   $72.00   $72.00  
  Purchase #2 $160.35   12.773%   $180.8315   $180.83   $180.85   $180.80  
  Purchase #3 $233.71   11.296%   $260.1099   $260.11   $260.10   $260.10  
  Purchase #4 $179.76   4.163%   $187.2434   $187.24   $187.25   $187.20  
  Purchase #5 $25.81   10.483%   $28.5157   $28.52   $28.50   $28.50  
  Purchase #6 $206.99   3.686%   $214.6197   $214.62   $214.60   $214.60  
  Purchase #7 $105.76   8.330%   $114.5698   $114.57   $114.55   $114.60  
  7 purchase totals = $981.95       $1,057.9110   $1,057.91   $1,057.85   $1,057.80