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	$89.84	9.439%	$98.32	$98.32	$98.30	$98.30
Purchase #2	$61.30	10.819%	$67.932	$67.93	$67.95	$67.90
Purchase #3	$94.84	13.797%	$107.9251	$107.93	$107.95	$107.90
Purchase #4	$20.68	5.317%	$21.7796	$21.78	$21.80	$21.80
Purchase #5	$216.43	5.807%	$228.9981	$229.00	$229.00	$229.00
Purchase #6	$39.44	6.816%	$42.1282	$42.13	$42.15	$42.10
Purchase #7	$79.25	13.294%	$89.7855	$89.79	$89.80	$89.80
7 purchase totals =	$601.78		$656.8685	$656.88	$656.95	$656.80