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	$228.56	12.340%	$256.7643	$256.76	$256.75	$256.80
Purchase #2	$181.62	7.611%	$195.4431	$195.44	$195.45	$195.40
Purchase #3	$148.47	10.494%	$164.0504	$164.05	$164.05	$164.10
Purchase #4	$216.78	12.530%	$243.9425	$243.94	$243.95	$243.90
Purchase #5	$133.86	6.551%	$142.6292	$142.63	$142.65	$142.60
Purchase #6	$125.79	4.181%	$131.0493	$131.05	$131.05	$131.00
Purchase #7	$120.61	5.726%	$127.5161	$127.52	$127.50	$127.50
7 purchase totals =	$1,155.69		$1,261.3949	$1,261.39	$1,261.40	$1,261.30