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	$247.63	11.570%	$276.2808	$276.28	$276.30	$276.30
Purchase #2	$38.61	10.502%	$42.6648	$42.66	$42.65	$42.70
Purchase #3	$225.75	3.392%	$233.4074	$233.41	$233.40	$233.40
Purchase #4	$54.58	12.383%	$61.3386	$61.34	$61.35	$61.30
Purchase #5	$170.95	5.661%	$180.6275	$180.63	$180.65	$180.60
Purchase #6	$67.44	4.279%	$70.3258	$70.33	$70.35	$70.30
Purchase #7	$187.43	4.563%	$195.9824	$195.98	$196.00	$196.00
7 purchase totals =	$992.39		$1,060.6273	$1,060.63	$1,060.70	$1,060.60