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	$28.49	10.212%	$31.3994	$31.40	$31.40	$31.40
Purchase #2	$78.76	13.842%	$89.662	$89.66	$89.65	$89.70
Purchase #3	$78.62	5.703%	$83.1037	$83.10	$83.10	$83.10
Purchase #4	$234.36	6.567%	$249.7504	$249.75	$249.75	$249.80
Purchase #5	$39.84	10.817%	$44.1495	$44.15	$44.15	$44.10
Purchase #6	$211.42	13.711%	$240.4078	$240.41	$240.40	$240.40
Purchase #7	$99.28	10.614%	$109.8176	$109.82	$109.80	$109.80
7 purchase totals =	$770.77		$848.2904	$848.29	$848.25	$848.30