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 $239.26   5.404%   $252.1896   $252.19   $252.20   $252.20  
  Purchase #2 $226.55   7.492%   $243.5231   $243.52   $243.50   $243.50  
  Purchase #3 $84.76   12.668%   $95.4974   $95.50   $95.50   $95.50  
  Purchase #4 $114.77   13.276%   $130.0069   $130.01   $130.00   $130.00  
  Purchase #5 $188.27   9.572%   $206.2912   $206.29   $206.30   $206.30  
  Purchase #6 $212.60   13.376%   $241.0374   $241.04   $241.05   $241.00  
  Purchase #7 $60.36   10.337%   $66.5994   $66.60   $66.60   $66.60  
  7 purchase totals = $1,126.57       $1,235.1450   $1,235.15   $1,235.15   $1,235.10