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 $208.61   11.698%   $233.0132   $233.01   $233.00   $233.00  
  Purchase #2 $235.99   6.359%   $250.9966   $251.00   $251.00   $251.00  
  Purchase #3 $246.74   8.763%   $268.3618   $268.36   $268.35   $268.40  
  Purchase #4 $149.84   9.728%   $164.4164   $164.42   $164.40   $164.40  
  Purchase #5 $42.35   11.613%   $47.2681   $47.27   $47.25   $47.30  
  Purchase #6 $45.84   8.843%   $49.8936   $49.89   $49.90   $49.90  
  Purchase #7 $210.51   8.292%   $227.9655   $227.97   $227.95   $228.00  
  7 purchase totals = $1,139.88       $1,241.9152   $1,241.92   $1,241.85   $1,242.00