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 $240.72   9.548%   $263.7039   $263.70   $263.70   $263.70  
  Purchase #2 $57.67   4.202%   $60.0933   $60.09   $60.10   $60.10  
  Purchase #3 $101.48   3.497%   $105.0288   $105.03   $105.05   $105.00  
  Purchase #4 $153.53   5.787%   $162.4148   $162.41   $162.40   $162.40  
  Purchase #5 $206.89   13.702%   $235.2381   $235.24   $235.25   $235.20  
  Purchase #6 $142.53   9.538%   $156.1245   $156.12   $156.10   $156.10  
  Purchase #7 $77.79   10.831%   $86.2154   $86.22   $86.20   $86.20  
  7 purchase totals = $980.61       $1,068.8188   $1,068.81   $1,068.80   $1,068.70