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 $246.32   10.439%   $272.0333   $272.03   $272.05   $272.00  
  Purchase #2 $124.29   6.571%   $132.4571   $132.46   $132.45   $132.50  
  Purchase #3 $167.91   11.363%   $186.9896   $186.99   $187.00   $187.00  
  Purchase #4 $190.81   13.484%   $216.5388   $216.54   $216.55   $216.50  
  Purchase #5 $202.90   13.556%   $230.4051   $230.41   $230.40   $230.40  
  Purchase #6 $209.40   10.725%   $231.8582   $231.86   $231.85   $231.90  
  Purchase #7 $202.30   7.868%   $218.217   $218.22   $218.20   $218.20  
  7 purchase totals = $1,343.93       $1,488.4991   $1,488.51   $1,488.50   $1,488.50