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 $57.68   3.316%   $59.5927   $59.59   $59.60   $59.60  
  Purchase #2 $218.69   7.722%   $235.5772   $235.58   $235.60   $235.60  
  Purchase #3 $175.40   9.551%   $192.1525   $192.15   $192.15   $192.20  
  Purchase #4 $80.29   3.387%   $83.0094   $83.01   $83.00   $83.00  
  Purchase #5 $96.26   4.598%   $100.686   $100.69   $100.70   $100.70  
  Purchase #6 $250.94   5.603%   $265.0002   $265.00   $265.00   $265.00  
  Purchase #7 $199.51   8.368%   $216.205   $216.21   $216.20   $216.20  
  7 purchase totals = $1,078.77       $1,152.2230   $1,152.23   $1,152.25   $1,152.30