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	$78.94	6.726%	$84.2495	$84.25	$84.25	$84.20
Purchase #2	$99.63	10.690%	$110.2804	$110.28	$110.30	$110.30
Purchase #3	$28.54	10.499%	$31.5364	$31.54	$31.55	$31.50
Purchase #4	$208.47	8.323%	$225.821	$225.82	$225.80	$225.80
Purchase #5	$240.28	4.310%	$250.6361	$250.64	$250.65	$250.60
Purchase #6	$229.45	12.623%	$258.4135	$258.41	$258.40	$258.40
Purchase #7	$41.27	9.841%	$45.3314	$45.33	$45.35	$45.30
7 purchase totals =	$926.58		$1,006.2683	$1,006.27	$1,006.30	$1,006.10