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 $201.74   12.808%   $227.5789   $227.58   $227.60   $227.60  
  Purchase #2 $43.38   13.183%   $49.0988   $49.10   $49.10   $49.10  
  Purchase #3 $150.61   8.687%   $163.6935   $163.69   $163.70   $163.70  
  Purchase #4 $42.89   9.812%   $47.0984   $47.10   $47.10   $47.10  
  Purchase #5 $242.42   10.772%   $268.5335   $268.53   $268.55   $268.50  
  Purchase #6 $168.73   5.823%   $178.5551   $178.56   $178.55   $178.60  
  Purchase #7 $242.55   11.828%   $271.2388   $271.24   $271.25   $271.20  
  7 purchase totals = $1,092.32       $1,205.7970   $1,205.80   $1,205.85   $1,205.80