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	$35.90	7.375%	$38.5476	$38.55	$38.55	$38.50
Purchase #2	$152.69	10.858%	$169.2691	$169.27	$169.25	$169.30
Purchase #3	$101.72	7.141%	$108.9838	$108.98	$109.00	$109.00
Purchase #4	$101.81	7.744%	$109.6942	$109.69	$109.70	$109.70
Purchase #5	$111.99	10.582%	$123.8408	$123.84	$123.85	$123.80
Purchase #6	$143.55	4.470%	$149.9667	$149.97	$149.95	$150.00
Purchase #7	$214.34	4.263%	$223.4773	$223.48	$223.50	$223.50
7 purchase totals =	$862.00		$923.7795	$923.78	$923.80	$923.80