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	$79.81	12.713%	$89.9562	$89.96	$89.95	$90.00
Purchase #2	$89.52	12.342%	$100.5686	$100.57	$100.55	$100.60
Purchase #3	$82.83	7.648%	$89.1648	$89.16	$89.15	$89.20
Purchase #4	$229.75	12.407%	$258.2551	$258.26	$258.25	$258.30
Purchase #5	$125.49	12.220%	$140.8249	$140.82	$140.80	$140.80
Purchase #6	$209.96	12.269%	$235.72	$235.72	$235.70	$235.70
Purchase #7	$232.43	11.327%	$258.7573	$258.76	$258.75	$258.80
7 purchase totals =	$1,049.79		$1,173.2469	$1,173.25	$1,173.15	$1,173.40