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	$80.35	3.151%	$82.8818	$82.88	$82.90	$82.90
Purchase #2	$144.88	9.400%	$158.4987	$158.50	$158.50	$158.50
Purchase #3	$35.46	5.819%	$37.5234	$37.52	$37.50	$37.50
Purchase #4	$245.91	10.158%	$270.8895	$270.89	$270.90	$270.90
Purchase #5	$26.94	6.675%	$28.7382	$28.74	$28.75	$28.70
Purchase #6	$179.34	9.717%	$196.7665	$196.77	$196.75	$196.80
Purchase #7	$194.99	10.869%	$216.1835	$216.18	$216.20	$216.20
7 purchase totals =	$907.87		$991.4816	$991.48	$991.50	$991.50