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 $48.70   8.576%   $52.8765   $52.88   $52.90   $52.90  
  Purchase #2 $193.43   10.494%   $213.7285   $213.73   $213.75   $213.70  
  Purchase #3 $198.40   4.815%   $207.953   $207.95   $207.95   $208.00  
  Purchase #4 $150.60   7.564%   $161.9914   $161.99   $162.00   $162.00  
  Purchase #5 $241.60   4.141%   $251.6047   $251.60   $251.60   $251.60  
  Purchase #6 $166.52   5.260%   $175.279   $175.28   $175.30   $175.30  
  Purchase #7 $237.93   13.466%   $269.9697   $269.97   $269.95   $270.00  
  7 purchase totals = $1,237.18       $1,333.4028   $1,333.40   $1,333.45   $1,333.50