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	$31.43	7.858%	$33.8998	$33.90	$33.90	$33.90
Purchase #2	$222.81	5.521%	$235.1113	$235.11	$235.10	$235.10
Purchase #3	$114.44	4.229%	$119.2797	$119.28	$119.30	$119.30
Purchase #4	$95.57	4.548%	$99.9165	$99.92	$99.90	$99.90
Purchase #5	$147.84	12.654%	$166.5477	$166.55	$166.55	$166.50
Purchase #6	$240.98	12.449%	$270.9796	$270.98	$271.00	$271.00
Purchase #7	$81.75	9.856%	$89.8073	$89.81	$89.80	$89.80
7 purchase totals =	$934.82		$1,015.5419	$1,015.55	$1,015.55	$1,015.50