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 $227.58   6.584%   $242.5639   $242.56   $242.55   $242.60  
  Purchase #2 $169.56   12.314%   $190.4396   $190.44   $190.45   $190.40  
  Purchase #3 $134.47   4.608%   $140.6664   $140.67   $140.65   $140.70  
  Purchase #4 $212.76   9.186%   $232.3041   $232.30   $232.30   $232.30  
  Purchase #5 $86.38   9.363%   $94.4678   $94.47   $94.45   $94.50  
  Purchase #6 $55.51   6.451%   $59.091   $59.09   $59.10   $59.10  
  Purchase #7 $68.92   6.354%   $73.2992   $73.30   $73.30   $73.30  
  7 purchase totals = $955.18       $1,032.8320   $1,032.83   $1,032.80   $1,032.90