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 $108.41   12.544%   $122.009   $122.01   $122.00   $122.00  
  Purchase #2 $119.46   9.801%   $131.1683   $131.17   $131.15   $131.20  
  Purchase #3 $216.89   11.806%   $242.496   $242.50   $242.50   $242.50  
  Purchase #4 $166.73   4.656%   $174.4929   $174.49   $174.50   $174.50  
  Purchase #5 $11.50   6.357%   $12.2311   $12.23   $12.25   $12.20  
  Purchase #6 $49.69   12.527%   $55.9147   $55.91   $55.90   $55.90  
  Purchase #7 $240.87   10.754%   $266.7732   $266.77   $266.75   $266.80  
  7 purchase totals = $913.55       $1,005.0852   $1,005.08   $1,005.05   $1,005.10