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	$77.31	6.687%	$82.4797	$82.48	$82.50	$82.50
Purchase #2	$23.43	9.759%	$25.7165	$25.72	$25.70	$25.70
Purchase #3	$96.54	10.153%	$106.3417	$106.34	$106.35	$106.30
Purchase #4	$220.74	13.665%	$250.9041	$250.90	$250.90	$250.90
Purchase #5	$39.56	6.293%	$42.0495	$42.05	$42.05	$42.00
Purchase #6	$11.77	7.324%	$12.632	$12.63	$12.65	$12.60
Purchase #7	$51.27	3.303%	$52.9634	$52.96	$52.95	$53.00
7 purchase totals =	$520.62		$573.0869	$573.08	$573.10	$573.00