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	$105.43	12.829%	$118.9556	$118.96	$118.95	$119.00
Purchase #2	$84.71	6.504%	$90.2195	$90.22	$90.20	$90.20
Purchase #3	$120.90	7.608%	$130.0981	$130.10	$130.10	$130.10
Purchase #4	$232.76	12.268%	$261.315	$261.32	$261.30	$261.30
Purchase #5	$150.87	10.346%	$166.479	$166.48	$166.50	$166.50
Purchase #6	$115.85	10.474%	$127.9841	$127.98	$128.00	$128.00
Purchase #7	$35.64	12.467%	$40.0832	$40.08	$40.10	$40.10
7 purchase totals =	$846.16		$935.1345	$935.14	$935.15	$935.20