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	$37.30	6.608%	$39.7648	$39.76	$39.75	$39.80
Purchase #2	$234.63	12.794%	$264.6486	$264.65	$264.65	$264.60
Purchase #3	$39.45	3.735%	$40.9235	$40.92	$40.90	$40.90
Purchase #4	$181.49	5.148%	$190.8331	$190.83	$190.85	$190.80
Purchase #5	$61.29	9.361%	$67.0274	$67.03	$67.05	$67.00
Purchase #6	$165.98	10.705%	$183.7482	$183.75	$183.75	$183.70
Purchase #7	$37.46	7.504%	$40.271	$40.27	$40.25	$40.30
7 purchase totals =	$757.60		$827.2166	$827.21	$827.20	$827.10