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	$143.54	11.116%	$159.4959	$159.50	$159.50	$159.50
Purchase #2	$250.28	7.799%	$269.7993	$269.80	$269.80	$269.80
Purchase #3	$63.96	13.315%	$72.4763	$72.48	$72.50	$72.50
Purchase #4	$61.78	4.397%	$64.4965	$64.50	$64.50	$64.50
Purchase #5	$181.32	9.620%	$198.763	$198.76	$198.75	$198.80
Purchase #6	$181.56	5.828%	$192.1413	$192.14	$192.15	$192.10
Purchase #7	$160.83	9.297%	$175.7824	$175.78	$175.80	$175.80
7 purchase totals =	$1,043.27		$1,132.9547	$1,132.96	$1,133.00	$1,133.00