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	$243.41	9.174%	$265.7404	$265.74	$265.75	$265.70
Purchase #2	$49.43	6.360%	$52.5737	$52.57	$52.55	$52.60
Purchase #3	$247.36	6.738%	$264.0271	$264.03	$264.05	$264.00
Purchase #4	$131.80	4.181%	$137.3106	$137.31	$137.30	$137.30
Purchase #5	$79.27	4.284%	$82.6659	$82.67	$82.65	$82.70
Purchase #6	$11.42	12.217%	$12.8152	$12.82	$12.80	$12.80
Purchase #7	$131.31	9.130%	$143.2986	$143.30	$143.30	$143.30
7 purchase totals =	$894.00		$958.4315	$958.44	$958.40	$958.40