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 $237.25   10.667%   $262.5575   $262.56   $262.55   $262.60  
  Purchase #2 $77.35   4.222%   $80.6157   $80.62   $80.60   $80.60  
  Purchase #3 $141.83   5.266%   $149.2988   $149.30   $149.30   $149.30  
  Purchase #4 $162.87   10.549%   $180.0512   $180.05   $180.05   $180.10  
  Purchase #5 $246.91   4.619%   $258.3148   $258.31   $258.30   $258.30  
  Purchase #6 $35.65   12.459%   $40.0916   $40.09   $40.10   $40.10  
  Purchase #7 $47.91   9.678%   $52.5467   $52.55   $52.55   $52.50  
  7 purchase totals = $949.77       $1,023.4763   $1,023.48   $1,023.45   $1,023.50