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	$242.70	3.556%	$251.3304	$251.33	$251.35	$251.30
Purchase #2	$85.54	6.251%	$90.8871	$90.89	$90.90	$90.90
Purchase #3	$19.86	12.705%	$22.3832	$22.38	$22.40	$22.40
Purchase #4	$67.57	13.747%	$76.8588	$76.86	$76.85	$76.90
Purchase #5	$80.54	9.388%	$88.1011	$88.10	$88.10	$88.10
Purchase #6	$99.50	10.323%	$109.7714	$109.77	$109.75	$109.80
Purchase #7	$101.98	8.191%	$110.3332	$110.33	$110.35	$110.30
7 purchase totals =	$697.69		$749.6652	$749.66	$749.70	$749.70