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 $202.35   3.113%   $208.6492   $208.65   $208.65   $208.60  
  Purchase #2 $54.63   5.526%   $57.6489   $57.65   $57.65   $57.60  
  Purchase #3 $126.28   10.137%   $139.081   $139.08   $139.10   $139.10  
  Purchase #4 $147.65   10.229%   $162.7531   $162.75   $162.75   $162.80  
  Purchase #5 $53.56   7.471%   $57.5615   $57.56   $57.55   $57.60  
  Purchase #6 $113.85   11.451%   $126.887   $126.89   $126.90   $126.90  
  Purchase #7 $200.27   6.217%   $212.7208   $212.72   $212.70   $212.70  
  7 purchase totals = $898.59       $965.3015   $965.30   $965.30   $965.30