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 $227.84   10.703%   $252.2257   $252.23   $252.25   $252.20  
  Purchase #2 $5.59   10.129%   $6.1562   $6.16   $6.15   $6.20  
  Purchase #3 $226.75   9.343%   $247.9353   $247.94   $247.95   $247.90  
  Purchase #4 $165.97   10.124%   $182.7728   $182.77   $182.75   $182.80  
  Purchase #5 $66.37   5.205%   $69.8246   $69.82   $69.80   $69.80  
  Purchase #6 $92.89   9.112%   $101.3541   $101.35   $101.35   $101.40  
  Purchase #7 $140.90   9.292%   $153.9924   $153.99   $154.00   $154.00  
  7 purchase totals = $926.31       $1,014.2611   $1,014.26   $1,014.25   $1,014.30