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 $82.31   13.611%   $93.5132   $93.51   $93.50   $93.50  
  Purchase #2 $114.86   7.572%   $123.5572   $123.56   $123.55   $123.60  
  Purchase #3 $229.76   9.241%   $250.9921   $250.99   $251.00   $251.00  
  Purchase #4 $90.52   3.871%   $94.024   $94.02   $94.00   $94.00  
  Purchase #5 $246.28   13.434%   $279.3653   $279.37   $279.35   $279.40  
  Purchase #6 $249.93   10.548%   $276.2926   $276.29   $276.30   $276.30  
  Purchase #7 $167.71   9.254%   $183.2299   $183.23   $183.25   $183.20  
  7 purchase totals = $1,181.37       $1,300.9743   $1,300.97   $1,300.95   $1,301.00