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 $231.81   11.274%   $257.9443   $257.94   $257.95   $257.90  
  Purchase #2 $73.86   10.677%   $81.746   $81.75   $81.75   $81.70  
  Purchase #3 $131.95   9.377%   $144.323   $144.32   $144.30   $144.30  
  Purchase #4 $192.59   10.759%   $213.3108   $213.31   $213.30   $213.30  
  Purchase #5 $145.75   11.603%   $162.6614   $162.66   $162.65   $162.70  
  Purchase #6 $33.59   7.437%   $36.0881   $36.09   $36.10   $36.10  
  Purchase #7 $237.77   12.710%   $267.9906   $267.99   $268.00   $268.00  
  7 purchase totals = $1,047.32       $1,164.0642   $1,164.06   $1,164.05   $1,164.00