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 $124.93   4.831%   $130.9654   $130.97   $130.95   $131.00  
  Purchase #2 $239.50   9.214%   $261.5675   $261.57   $261.55   $261.60  
  Purchase #3 $167.25   4.679%   $175.0756   $175.08   $175.10   $175.10  
  Purchase #4 $17.31   4.153%   $18.0289   $18.03   $18.05   $18.00  
  Purchase #5 $189.65   4.154%   $197.5281   $197.53   $197.55   $197.50  
  Purchase #6 $201.51   3.134%   $207.8253   $207.83   $207.85   $207.80  
  Purchase #7 $189.93   10.757%   $210.3608   $210.36   $210.35   $210.40  
  7 purchase totals = $1,130.08       $1,201.3516   $1,201.37   $1,201.40   $1,201.40