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 $142.44   7.656%   $153.3452   $153.35   $153.35   $153.30  
  Purchase #2 $53.49   8.790%   $58.1918   $58.19   $58.20   $58.20  
  Purchase #3 $183.84   10.470%   $203.088   $203.09   $203.10   $203.10  
  Purchase #4 $68.30   4.839%   $71.605   $71.61   $71.60   $71.60  
  Purchase #5 $163.38   10.358%   $180.3029   $180.30   $180.30   $180.30  
  Purchase #6 $169.82   8.544%   $184.3294   $184.33   $184.35   $184.30  
  Purchase #7 $224.76   5.383%   $236.8588   $236.86   $236.85   $236.90  
  7 purchase totals = $1,006.03       $1,087.7211   $1,087.73   $1,087.75   $1,087.70