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	$221.33	7.803%	$238.6004	$238.60	$238.60	$238.60
Purchase #2	$75.51	9.649%	$82.796	$82.80	$82.80	$82.80
Purchase #3	$62.50	6.435%	$66.5219	$66.52	$66.50	$66.50
Purchase #4	$162.89	13.503%	$184.885	$184.89	$184.90	$184.90
Purchase #5	$197.60	6.512%	$210.4677	$210.47	$210.45	$210.50
Purchase #6	$83.51	9.720%	$91.6272	$91.63	$91.65	$91.60
Purchase #7	$86.44	9.386%	$94.5533	$94.55	$94.55	$94.60
7 purchase totals =	$889.78		$969.4515	$969.46	$969.45	$969.50