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 $56.83   5.235%   $59.8051   $59.81   $59.80   $59.80  
  Purchase #2 $241.31   4.830%   $252.9653   $252.97   $252.95   $253.00  
  Purchase #3 $142.33   7.613%   $153.1656   $153.17   $153.15   $153.20  
  Purchase #4 $199.39   6.780%   $212.9086   $212.91   $212.90   $212.90  
  Purchase #5 $244.90   9.500%   $268.1655   $268.17   $268.15   $268.20  
  Purchase #6 $171.61   8.379%   $185.9892   $185.99   $186.00   $186.00  
  Purchase #7 $57.84   7.528%   $62.1942   $62.19   $62.20   $62.20  
  7 purchase totals = $1,114.21       $1,195.1935   $1,195.21   $1,195.15   $1,195.30