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 $226.41   8.772%   $246.2707   $246.27   $246.25   $246.30  
  Purchase #2 $193.55   13.386%   $219.4586   $219.46   $219.45   $219.50  
  Purchase #3 $103.32   5.127%   $108.6172   $108.62   $108.60   $108.60  
  Purchase #4 $33.77   11.460%   $37.64   $37.64   $37.65   $37.60  
  Purchase #5 $243.93   10.133%   $268.6474   $268.65   $268.65   $268.60  
  Purchase #6 $46.83   4.541%   $48.9566   $48.96   $48.95   $49.00  
  Purchase #7 $192.93   7.272%   $206.9599   $206.96   $206.95   $207.00  
  7 purchase totals = $1,040.74       $1,136.5504   $1,136.56   $1,136.50   $1,136.60