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 $5.32   13.523%   $6.0394   $6.04   $6.05   $6.00  
  Purchase #2 $165.87   11.672%   $185.2303   $185.23   $185.25   $185.20  
  Purchase #3 $10.76   7.780%   $11.5971   $11.60   $11.60   $11.60  
  Purchase #4 $247.42   6.219%   $262.807   $262.81   $262.80   $262.80  
  Purchase #5 $199.30   8.663%   $216.5654   $216.57   $216.55   $216.60  
  Purchase #6 $128.98   7.697%   $138.9076   $138.91   $138.90   $138.90  
  Purchase #7 $186.75   3.382%   $193.0659   $193.07   $193.05   $193.10  
  7 purchase totals = $944.40       $1,014.2127   $1,014.23   $1,014.20   $1,014.20