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	$96.85	10.370%	$106.8933	$106.89	$106.90	$106.90
Purchase #2	$192.56	4.353%	$200.9421	$200.94	$200.95	$200.90
Purchase #3	$186.88	13.507%	$212.1219	$212.12	$212.10	$212.10
Purchase #4	$209.39	10.322%	$231.0032	$231.00	$231.00	$231.00
Purchase #5	$63.39	10.836%	$70.2589	$70.26	$70.25	$70.30
Purchase #6	$112.55	4.316%	$117.4077	$117.41	$117.40	$117.40
Purchase #7	$223.78	10.515%	$247.3105	$247.31	$247.30	$247.30
7 purchase totals =	$1,085.40		$1,185.9376	$1,185.93	$1,185.90	$1,185.90