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 $233.73   13.846%   $266.0923   $266.09   $266.10   $266.10  
  Purchase #2 $168.79   4.443%   $176.2893   $176.29   $176.30   $176.30  
  Purchase #3 $101.34   10.170%   $111.6463   $111.65   $111.65   $111.60  
  Purchase #4 $220.86   6.702%   $235.662   $235.66   $235.65   $235.70  
  Purchase #5 $95.68   4.182%   $99.6813   $99.68   $99.70   $99.70  
  Purchase #6 $246.66   13.168%   $279.1402   $279.14   $279.15   $279.10  
  Purchase #7 $214.49   5.339%   $225.9416   $225.94   $225.95   $225.90  
  7 purchase totals = $1,281.55       $1,394.4530   $1,394.45   $1,394.50   $1,394.40