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	$54.76	9.419%	$59.9178	$59.92	$59.90	$59.90
Purchase #2	$240.85	13.775%	$274.0271	$274.03	$274.05	$274.00
Purchase #3	$157.81	8.704%	$171.5458	$171.55	$171.55	$171.50
Purchase #4	$195.56	13.440%	$221.8433	$221.84	$221.85	$221.80
Purchase #5	$154.52	5.316%	$162.7343	$162.73	$162.75	$162.70
Purchase #6	$144.33	5.543%	$152.3302	$152.33	$152.35	$152.30
Purchase #7	$42.73	5.409%	$45.0413	$45.04	$45.05	$45.00
7 purchase totals =	$990.56		$1,087.4398	$1,087.44	$1,087.50	$1,087.20