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 $46.98   11.307%   $52.292   $52.29   $52.30   $52.30  
  Purchase #2 $162.88   11.520%   $181.6438   $181.64   $181.65   $181.60  
  Purchase #3 $70.71   10.116%   $77.863   $77.86   $77.85   $77.90  
  Purchase #4 $189.97   8.515%   $206.1459   $206.15   $206.15   $206.10  
  Purchase #5 $132.73   6.822%   $141.7848   $141.78   $141.80   $141.80  
  Purchase #6 $114.95   13.826%   $130.843   $130.84   $130.85   $130.80  
  Purchase #7 $96.93   9.859%   $106.4863   $106.49   $106.50   $106.50  
  7 purchase totals = $815.15       $897.0588   $897.05   $897.10   $897.00