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	$149.64	13.257%	$169.4778	$169.48	$169.50	$169.50
Purchase #2	$94.47	5.663%	$99.8198	$99.82	$99.80	$99.80
Purchase #3	$114.37	3.371%	$118.2254	$118.23	$118.25	$118.20
Purchase #4	$131.84	6.546%	$140.4702	$140.47	$140.45	$140.50
Purchase #5	$207.28	8.512%	$224.9237	$224.92	$224.90	$224.90
Purchase #6	$75.70	6.844%	$80.8809	$80.88	$80.90	$80.90
Purchase #7	$69.37	13.216%	$78.5379	$78.54	$78.55	$78.50
7 purchase totals =	$842.67		$912.3357	$912.34	$912.35	$912.30