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	$25.30	4.237%	$26.372	$26.37	$26.35	$26.40
Purchase #2	$233.53	8.496%	$253.3707	$253.37	$253.35	$253.40
Purchase #3	$141.56	3.869%	$147.037	$147.04	$147.05	$147.00
Purchase #4	$40.90	4.365%	$42.6853	$42.69	$42.70	$42.70
Purchase #5	$19.57	3.490%	$20.253	$20.25	$20.25	$20.30
Purchase #6	$240.96	4.141%	$250.9382	$250.94	$250.95	$250.90
Purchase #7	$67.34	9.304%	$73.6053	$73.61	$73.60	$73.60
7 purchase totals =	$769.16		$814.2615	$814.27	$814.25	$814.30