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	$219.53	3.546%	$227.3145	$227.31	$227.30	$227.30
Purchase #2	$109.61	5.636%	$115.7876	$115.79	$115.80	$115.80
Purchase #3	$163.48	11.472%	$182.2344	$182.23	$182.25	$182.20
Purchase #4	$99.67	3.574%	$103.2322	$103.23	$103.25	$103.20
Purchase #5	$80.69	11.404%	$89.8919	$89.89	$89.90	$89.90
Purchase #6	$54.25	12.350%	$60.9499	$60.95	$60.95	$60.90
Purchase #7	$50.44	10.437%	$55.7044	$55.70	$55.70	$55.70
7 purchase totals =	$777.67		$835.1149	$835.10	$835.15	$835.00