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	$156.85	9.354%	$171.5217	$171.52	$171.50	$171.50
Purchase #2	$5.35	8.864%	$5.8242	$5.82	$5.80	$5.80
Purchase #3	$249.84	5.755%	$264.2183	$264.22	$264.20	$264.20
Purchase #4	$50.59	9.276%	$55.2827	$55.28	$55.30	$55.30
Purchase #5	$243.92	12.229%	$273.749	$273.75	$273.75	$273.70
Purchase #6	$236.64	12.276%	$265.6899	$265.69	$265.70	$265.70
Purchase #7	$57.30	11.271%	$63.7583	$63.76	$63.75	$63.80
7 purchase totals =	$1,000.49		$1,100.0441	$1,100.04	$1,100.00	$1,100.00