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	$83.79	6.863%	$89.5405	$89.54	$89.55	$89.50
Purchase #2	$71.66	9.638%	$78.5666	$78.57	$78.55	$78.60
Purchase #3	$60.79	12.148%	$68.1748	$68.17	$68.15	$68.20
Purchase #4	$91.63	3.154%	$94.52	$94.52	$94.50	$94.50
Purchase #5	$192.46	12.139%	$215.8227	$215.82	$215.80	$215.80
Purchase #6	$200.51	5.662%	$211.8629	$211.86	$211.85	$211.90
Purchase #7	$217.53	11.435%	$242.4046	$242.40	$242.40	$242.40
7 purchase totals =	$918.37		$1,000.8921	$1,000.88	$1,000.80	$1,000.90