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 $9.49   7.814%   $10.2315   $10.23   $10.25   $10.20  
  Purchase #2 $143.94   12.601%   $162.0779   $162.08   $162.10   $162.10  
  Purchase #3 $78.36   11.531%   $87.3957   $87.40   $87.40   $87.40  
  Purchase #4 $29.62   3.504%   $30.6579   $30.66   $30.65   $30.70  
  Purchase #5 $231.34   10.242%   $255.0338   $255.03   $255.05   $255.00  
  Purchase #6 $128.86   6.653%   $137.4331   $137.43   $137.45   $137.40  
  Purchase #7 $140.66   7.588%   $151.3333   $151.33   $151.35   $151.30  
  7 purchase totals = $762.27       $834.1632   $834.16   $834.25   $834.10