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	$229.64	8.813%	$249.8782	$249.88	$249.90	$249.90
Purchase #2	$180.70	7.413%	$194.0953	$194.10	$194.10	$194.10
Purchase #3	$147.74	3.171%	$152.4248	$152.42	$152.40	$152.40
Purchase #4	$137.54	6.849%	$146.9601	$146.96	$146.95	$147.00
Purchase #5	$47.79	11.814%	$53.4359	$53.44	$53.45	$53.40
Purchase #6	$64.90	10.500%	$71.7145	$71.71	$71.70	$71.70
Purchase #7	$165.34	3.712%	$171.4774	$171.48	$171.50	$171.50
7 purchase totals =	$973.65		$1,039.9862	$1,039.99	$1,040.00	$1,040.00