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 $60.78   4.313%   $63.4014   $63.40   $63.40   $63.40  
  Purchase #2 $230.94   3.319%   $238.6049   $238.60   $238.60   $238.60  
  Purchase #3 $130.27   6.525%   $138.7701   $138.77   $138.75   $138.80  
  Purchase #4 $244.67   13.564%   $277.857   $277.86   $277.85   $277.90  
  Purchase #5 $68.38   11.192%   $76.0331   $76.03   $76.05   $76.00  
  Purchase #6 $103.60   5.160%   $108.9458   $108.95   $108.95   $108.90  
  Purchase #7 $157.56   5.460%   $166.1628   $166.16   $166.15   $166.20  
  7 purchase totals = $996.20       $1,069.7751   $1,069.77   $1,069.75   $1,069.80