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 $52.45   8.371%   $56.8406   $56.84   $56.85   $56.80  
  Purchase #2 $235.48   5.313%   $247.9911   $247.99   $248.00   $248.00  
  Purchase #3 $33.40   4.346%   $34.8516   $34.85   $34.85   $34.90  
  Purchase #4 $94.70   6.599%   $100.9493   $100.95   $100.95   $100.90  
  Purchase #5 $6.26   5.402%   $6.5982   $6.60   $6.60   $6.60  
  Purchase #6 $150.28   4.533%   $157.0922   $157.09   $157.10   $157.10  
  Purchase #7 $192.31   3.468%   $198.9793   $198.98   $199.00   $199.00  
  7 purchase totals = $764.88       $803.3023   $803.30   $803.35   $803.30