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	$136.33	3.755%	$141.4492	$141.45	$141.45	$141.40
Purchase #2	$199.71	12.150%	$223.9748	$223.97	$223.95	$224.00
Purchase #3	$109.85	6.258%	$116.7244	$116.72	$116.70	$116.70
Purchase #4	$167.49	10.555%	$185.1686	$185.17	$185.15	$185.20
Purchase #5	$136.41	11.302%	$151.8271	$151.83	$151.85	$151.80
Purchase #6	$178.42	3.751%	$185.1125	$185.11	$185.10	$185.10
Purchase #7	$206.36	5.174%	$217.0371	$217.04	$217.05	$217.00
7 purchase totals =	$1,134.57		$1,221.2937	$1,221.29	$1,221.25	$1,221.20