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 $63.66   10.258%   $70.1902   $70.19   $70.20   $70.20  
  Purchase #2 $38.61   8.104%   $41.739   $41.74   $41.75   $41.70  
  Purchase #3 $172.88   13.201%   $195.7019   $195.70   $195.70   $195.70  
  Purchase #4 $229.59   10.742%   $254.2526   $254.25   $254.25   $254.30  
  Purchase #5 $169.90   9.619%   $186.2427   $186.24   $186.25   $186.20  
  Purchase #6 $127.73   10.564%   $141.2234   $141.22   $141.20   $141.20  
  Purchase #7 $147.64   6.353%   $157.0196   $157.02   $157.00   $157.00  
  7 purchase totals = $950.01       $1,046.3694   $1,046.36   $1,046.35   $1,046.30