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	$100.89	8.159%	$109.1216	$109.12	$109.10	$109.10
Purchase #2	$39.25	12.490%	$44.1523	$44.15	$44.15	$44.20
Purchase #3	$196.82	12.517%	$221.456	$221.46	$221.45	$221.50
Purchase #4	$115.73	13.500%	$131.3536	$131.35	$131.35	$131.40
Purchase #5	$124.84	3.625%	$129.3655	$129.37	$129.35	$129.40
Purchase #6	$118.38	4.774%	$124.0315	$124.03	$124.05	$124.00
Purchase #7	$93.42	8.684%	$101.5326	$101.53	$101.55	$101.50
7 purchase totals =	$789.33		$861.0131	$861.01	$861.00	$861.10