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	$126.93	3.617%	$131.5211	$131.52	$131.50	$131.50
Purchase #2	$197.27	6.375%	$209.846	$209.85	$209.85	$209.80
Purchase #3	$227.77	3.264%	$235.2044	$235.20	$235.20	$235.20
Purchase #4	$198.71	11.604%	$221.7683	$221.77	$221.75	$221.80
Purchase #5	$221.95	3.486%	$229.6872	$229.69	$229.70	$229.70
Purchase #6	$61.96	7.801%	$66.7935	$66.79	$66.80	$66.80
Purchase #7	$85.57	4.640%	$89.5404	$89.54	$89.55	$89.50
7 purchase totals =	$1,120.16		$1,184.3609	$1,184.36	$1,184.35	$1,184.30