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 $5.76   11.722%   $6.4352   $6.44   $6.45   $6.40  
  Purchase #2 $245.30   11.509%   $273.5316   $273.53   $273.55   $273.50  
  Purchase #3 $57.76   5.393%   $60.875   $60.88   $60.90   $60.90  
  Purchase #4 $192.48   10.489%   $212.6692   $212.67   $212.65   $212.70  
  Purchase #5 $230.80   5.354%   $243.157   $243.16   $243.15   $243.20  
  Purchase #6 $92.33   12.407%   $103.7854   $103.79   $103.80   $103.80  
  Purchase #7 $166.71   5.295%   $175.5373   $175.54   $175.55   $175.50  
  7 purchase totals = $991.14       $1,075.9907   $1,076.01   $1,076.05   $1,076.00