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	$136.42	6.220%	$144.9053	$144.91	$144.90	$144.90
Purchase #2	$166.31	6.624%	$177.3264	$177.33	$177.35	$177.30
Purchase #3	$191.60	12.829%	$216.1804	$216.18	$216.20	$216.20
Purchase #4	$29.72	11.107%	$33.021	$33.02	$33.00	$33.00
Purchase #5	$200.83	7.164%	$215.2175	$215.22	$215.20	$215.20
Purchase #6	$148.92	12.573%	$167.6437	$167.64	$167.65	$167.60
Purchase #7	$206.80	4.112%	$215.3036	$215.30	$215.30	$215.30
7 purchase totals =	$1,080.60		$1,169.5979	$1,169.60	$1,169.60	$1,169.50