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	$77.29	5.773%	$81.752	$81.75	$81.75	$81.80
Purchase #2	$81.26	12.118%	$91.1071	$91.11	$91.10	$91.10
Purchase #3	$240.73	13.803%	$273.958	$273.96	$273.95	$274.00
Purchase #4	$226.88	5.135%	$238.5303	$238.53	$238.55	$238.50
Purchase #5	$214.59	3.179%	$221.4118	$221.41	$221.40	$221.40
Purchase #6	$6.96	13.402%	$7.8928	$7.89	$7.90	$7.90
Purchase #7	$171.25	6.131%	$181.7493	$181.75	$181.75	$181.70
7 purchase totals =	$1,018.96		$1,096.4013	$1,096.40	$1,096.40	$1,096.40