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	$171.79	11.344%	$191.2779	$191.28	$191.30	$191.30
Purchase #2	$238.89	3.752%	$247.8532	$247.85	$247.85	$247.90
Purchase #3	$37.47	12.114%	$42.0091	$42.01	$42.00	$42.00
Purchase #4	$72.28	3.118%	$74.5337	$74.53	$74.55	$74.50
Purchase #5	$233.72	6.660%	$249.2858	$249.29	$249.30	$249.30
Purchase #6	$197.82	6.756%	$211.1847	$211.18	$211.20	$211.20
Purchase #7	$109.52	5.518%	$115.5633	$115.56	$115.55	$115.60
7 purchase totals =	$1,061.49		$1,131.7077	$1,131.70	$1,131.75	$1,131.80