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	$85.47	4.492%	$89.3093	$89.31	$89.30	$89.30
Purchase #2	$232.36	9.593%	$254.6503	$254.65	$254.65	$254.70
Purchase #3	$48.39	13.719%	$55.0286	$55.03	$55.05	$55.00
Purchase #4	$203.76	9.791%	$223.7101	$223.71	$223.70	$223.70
Purchase #5	$155.36	8.642%	$168.7862	$168.79	$168.80	$168.80
Purchase #6	$224.46	11.568%	$250.4255	$250.43	$250.45	$250.40
Purchase #7	$89.49	9.463%	$97.9584	$97.96	$97.95	$98.00
7 purchase totals =	$1,039.29		$1,139.8684	$1,139.88	$1,139.90	$1,139.90