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	$89.26	12.633%	$100.5362	$100.54	$100.55	$100.50
Purchase #2	$232.89	4.504%	$243.3794	$243.38	$243.40	$243.40
Purchase #3	$77.32	7.219%	$82.9017	$82.90	$82.90	$82.90
Purchase #4	$214.88	4.648%	$224.8676	$224.87	$224.85	$224.90
Purchase #5	$181.89	12.218%	$204.1133	$204.11	$204.10	$204.10
Purchase #6	$213.47	12.671%	$240.5188	$240.52	$240.50	$240.50
Purchase #7	$94.40	7.338%	$101.3271	$101.33	$101.35	$101.30
7 purchase totals =	$1,104.11		$1,197.6441	$1,197.65	$1,197.65	$1,197.60