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 $244.70   8.724%   $266.0476   $266.05   $266.05   $266.00  
  Purchase #2 $141.38   8.829%   $153.8624   $153.86   $153.85   $153.90  
  Purchase #3 $69.95   8.613%   $75.9748   $75.97   $75.95   $76.00  
  Purchase #4 $22.35   11.196%   $24.8523   $24.85   $24.85   $24.90  
  Purchase #5 $137.92   8.448%   $149.5715   $149.57   $149.55   $149.60  
  Purchase #6 $144.70   13.373%   $164.0507   $164.05   $164.05   $164.10  
  Purchase #7 $156.81   11.452%   $174.7679   $174.77   $174.75   $174.80  
  7 purchase totals = $917.81       $1,009.1272   $1,009.12   $1,009.05   $1,009.30