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	$187.58	6.310%	$199.4163	$199.42	$199.40	$199.40
Purchase #2	$123.41	13.530%	$140.1074	$140.11	$140.10	$140.10
Purchase #3	$223.73	9.118%	$244.1297	$244.13	$244.15	$244.10
Purchase #4	$236.32	11.631%	$263.8064	$263.81	$263.80	$263.80
Purchase #5	$63.79	13.689%	$72.5222	$72.52	$72.50	$72.50
Purchase #6	$166.58	3.294%	$172.0671	$172.07	$172.05	$172.10
Purchase #7	$79.43	8.650%	$86.3007	$86.30	$86.30	$86.30
7 purchase totals =	$1,080.84		$1,178.3498	$1,178.36	$1,178.30	$1,178.30