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	$72.92	10.190%	$80.3505	$80.35	$80.35	$80.40
Purchase #2	$168.80	12.670%	$190.187	$190.19	$190.20	$190.20
Purchase #3	$65.98	8.798%	$71.7849	$71.78	$71.80	$71.80
Purchase #4	$76.44	9.331%	$83.5726	$83.57	$83.55	$83.60
Purchase #5	$220.90	13.316%	$250.315	$250.32	$250.30	$250.30
Purchase #6	$222.66	6.862%	$237.9389	$237.94	$237.95	$237.90
Purchase #7	$170.28	9.445%	$186.3629	$186.36	$186.35	$186.40
7 purchase totals =	$997.98		$1,100.5118	$1,100.51	$1,100.50	$1,100.60