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 $50.27   6.662%   $53.619   $53.62   $53.60   $53.60  
  Purchase #2 $182.40   5.463%   $192.3645   $192.36   $192.35   $192.40  
  Purchase #3 $48.65   10.333%   $53.677   $53.68   $53.70   $53.70  
  Purchase #4 $119.57   6.285%   $127.085   $127.09   $127.10   $127.10  
  Purchase #5 $248.35   4.225%   $258.8428   $258.84   $258.85   $258.80  
  Purchase #6 $173.84   3.748%   $180.3555   $180.36   $180.35   $180.40  
  Purchase #7 $145.41   5.313%   $153.1356   $153.14   $153.15   $153.10  
  7 purchase totals = $968.49       $1,019.0794   $1,019.09   $1,019.10   $1,019.10