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	$137.38	8.700%	$149.3321	$149.33	$149.35	$149.30
Purchase #2	$38.43	12.210%	$43.1223	$43.12	$43.10	$43.10
Purchase #3	$139.73	4.533%	$146.064	$146.06	$146.05	$146.10
Purchase #4	$247.47	6.166%	$262.729	$262.73	$262.75	$262.70
Purchase #5	$152.39	12.551%	$171.5165	$171.52	$171.50	$171.50
Purchase #6	$191.81	4.712%	$200.8481	$200.85	$200.85	$200.80
Purchase #7	$224.73	5.624%	$237.3688	$237.37	$237.35	$237.40
7 purchase totals =	$1,131.94		$1,210.9808	$1,210.98	$1,210.95	$1,210.90