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	$40.31	12.352%	$45.2891	$45.29	$45.30	$45.30
Purchase #2	$210.33	8.763%	$228.7612	$228.76	$228.75	$228.80
Purchase #3	$135.89	6.142%	$144.2364	$144.24	$144.25	$144.20
Purchase #4	$208.60	7.158%	$223.5316	$223.53	$223.55	$223.50
Purchase #5	$85.82	9.395%	$93.8828	$93.88	$93.90	$93.90
Purchase #6	$249.29	7.335%	$267.5754	$267.58	$267.60	$267.60
Purchase #7	$156.54	3.850%	$162.5668	$162.57	$162.55	$162.60
7 purchase totals =	$1,086.78		$1,165.8433	$1,165.85	$1,165.90	$1,165.90