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 $118.88   13.848%   $135.3425   $135.34   $135.35   $135.30  
  Purchase #2 $192.48   8.112%   $208.094   $208.09   $208.10   $208.10  
  Purchase #3 $43.53   10.609%   $48.1481   $48.15   $48.15   $48.10  
  Purchase #4 $109.67   5.222%   $115.397   $115.40   $115.40   $115.40  
  Purchase #5 $185.46   10.677%   $205.2616   $205.26   $205.25   $205.30  
  Purchase #6 $157.26   9.692%   $172.5016   $172.50   $172.50   $172.50  
  Purchase #7 $149.69   11.552%   $166.9822   $166.98   $167.00   $167.00  
  7 purchase totals = $956.97       $1,051.7270   $1,051.72   $1,051.75   $1,051.70