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	$37.53	13.710%	$42.6754	$42.68	$42.70	$42.70
Purchase #2	$92.78	3.717%	$96.2286	$96.23	$96.25	$96.20
Purchase #3	$192.72	11.182%	$214.27	$214.27	$214.25	$214.30
Purchase #4	$128.58	9.500%	$140.7951	$140.80	$140.80	$140.80
Purchase #5	$196.91	10.436%	$217.4595	$217.46	$217.45	$217.50
Purchase #6	$79.31	4.663%	$83.0082	$83.01	$83.00	$83.00
Purchase #7	$129.36	10.460%	$142.8911	$142.89	$142.90	$142.90
7 purchase totals =	$857.19		$937.3279	$937.34	$937.35	$937.40