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	$27.40	11.646%	$30.591	$30.59	$30.60	$30.60
Purchase #2	$170.52	11.392%	$189.9456	$189.95	$189.95	$189.90
Purchase #3	$193.72	8.453%	$210.0952	$210.10	$210.10	$210.10
Purchase #4	$250.48	4.337%	$261.3433	$261.34	$261.35	$261.30
Purchase #5	$105.85	3.814%	$109.8871	$109.89	$109.90	$109.90
Purchase #6	$76.39	8.215%	$82.6654	$82.67	$82.65	$82.70
Purchase #7	$196.43	13.569%	$223.0836	$223.08	$223.10	$223.10
7 purchase totals =	$1,020.79		$1,107.6112	$1,107.62	$1,107.65	$1,107.60