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	$55.63	6.274%	$59.1202	$59.12	$59.10	$59.10
Purchase #2	$143.44	6.535%	$152.8138	$152.81	$152.80	$152.80
Purchase #3	$117.35	5.219%	$123.4745	$123.47	$123.45	$123.50
Purchase #4	$223.35	12.261%	$250.7349	$250.73	$250.75	$250.70
Purchase #5	$66.64	9.210%	$72.7775	$72.78	$72.80	$72.80
Purchase #6	$233.49	10.618%	$258.282	$258.28	$258.30	$258.30
Purchase #7	$203.91	12.754%	$229.9167	$229.92	$229.90	$229.90
7 purchase totals =	$1,043.81		$1,147.1196	$1,147.11	$1,147.10	$1,147.10