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	$52.73	12.815%	$59.4873	$59.49	$59.50	$59.50
Purchase #2	$132.55	5.194%	$139.4346	$139.43	$139.45	$139.40
Purchase #3	$154.75	13.351%	$175.4107	$175.41	$175.40	$175.40
Purchase #4	$62.67	10.199%	$69.0617	$69.06	$69.05	$69.10
Purchase #5	$94.76	12.340%	$106.4534	$106.45	$106.45	$106.50
Purchase #6	$144.94	12.380%	$162.8836	$162.88	$162.90	$162.90
Purchase #7	$62.90	13.297%	$71.2638	$71.26	$71.25	$71.30
7 purchase totals =	$705.30		$783.9951	$783.98	$784.00	$784.10