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	$86.94	4.661%	$90.9923	$90.99	$91.00	$91.00
Purchase #2	$84.83	11.181%	$94.3148	$94.31	$94.30	$94.30
Purchase #3	$29.87	9.731%	$32.7766	$32.78	$32.80	$32.80
Purchase #4	$82.33	9.658%	$90.2814	$90.28	$90.30	$90.30
Purchase #5	$212.52	9.312%	$232.3099	$232.31	$232.30	$232.30
Purchase #6	$68.86	5.519%	$72.6604	$72.66	$72.65	$72.70
Purchase #7	$51.96	11.279%	$57.8206	$57.82	$57.80	$57.80
7 purchase totals =	$617.31		$671.1560	$671.15	$671.15	$671.20