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	$147.93	7.144%	$158.4981	$158.50	$158.50	$158.50
Purchase #2	$142.74	8.779%	$155.2711	$155.27	$155.25	$155.30
Purchase #3	$236.41	11.796%	$264.2969	$264.30	$264.30	$264.30
Purchase #4	$164.81	12.757%	$185.8348	$185.83	$185.85	$185.80
Purchase #5	$96.90	12.595%	$109.1046	$109.10	$109.10	$109.10
Purchase #6	$154.58	6.682%	$164.909	$164.91	$164.90	$164.90
Purchase #7	$146.29	7.691%	$157.5412	$157.54	$157.55	$157.50
7 purchase totals =	$1,089.66		$1,195.4557	$1,195.45	$1,195.45	$1,195.40