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 $248.59   5.381%   $261.9666   $261.97   $261.95   $262.00  
  Purchase #2 $184.25   5.791%   $194.9199   $194.92   $194.90   $194.90  
  Purchase #3 $151.38   6.216%   $160.7898   $160.79   $160.80   $160.80  
  Purchase #4 $40.96   8.787%   $44.5592   $44.56   $44.55   $44.60  
  Purchase #5 $215.63   10.683%   $238.6658   $238.67   $238.65   $238.70  
  Purchase #6 $56.48   10.477%   $62.3974   $62.40   $62.40   $62.40  
  Purchase #7 $202.36   13.692%   $230.0671   $230.07   $230.05   $230.10  
  7 purchase totals = $1,099.65       $1,193.3658   $1,193.38   $1,193.30   $1,193.50