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	$145.31	7.192%	$155.7607	$155.76	$155.75	$155.80
Purchase #2	$104.51	5.150%	$109.8923	$109.89	$109.90	$109.90
Purchase #3	$87.66	9.805%	$96.2551	$96.26	$96.25	$96.30
Purchase #4	$105.33	4.727%	$110.3089	$110.31	$110.30	$110.30
Purchase #5	$236.92	10.609%	$262.0548	$262.05	$262.05	$262.10
Purchase #6	$33.89	5.601%	$35.7882	$35.79	$35.80	$35.80
Purchase #7	$205.68	11.443%	$229.216	$229.22	$229.20	$229.20
7 purchase totals =	$919.30		$999.2760	$999.28	$999.25	$999.40