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	$168.31	13.371%	$190.8147	$190.81	$190.80	$190.80
Purchase #2	$142.58	5.600%	$150.5645	$150.56	$150.55	$150.60
Purchase #3	$29.34	10.554%	$32.4365	$32.44	$32.45	$32.40
Purchase #4	$180.98	6.544%	$192.8233	$192.82	$192.80	$192.80
Purchase #5	$90.65	11.400%	$100.9841	$100.98	$101.00	$101.00
Purchase #6	$98.43	11.577%	$109.8252	$109.83	$109.85	$109.80
Purchase #7	$96.60	9.779%	$106.0465	$106.05	$106.05	$106.00
7 purchase totals =	$806.89		$883.4948	$883.49	$883.50	$883.40