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 $227.96   13.176%   $257.996   $258.00   $258.00   $258.00  
  Purchase #2 $174.95   5.748%   $185.0061   $185.01   $185.00   $185.00  
  Purchase #3 $71.39   11.430%   $79.5499   $79.55   $79.55   $79.50  
  Purchase #4 $102.59   11.645%   $114.5366   $114.54   $114.55   $114.50  
  Purchase #5 $181.25   12.581%   $204.0531   $204.05   $204.05   $204.10  
  Purchase #6 $79.72   6.573%   $84.96   $84.96   $84.95   $85.00  
  Purchase #7 $235.79   6.408%   $250.8994   $250.90   $250.90   $250.90  
  7 purchase totals = $1,073.65       $1,177.0011   $1,177.01   $1,177.00   $1,177.00