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	$230.83	6.813%	$246.5564	$246.56	$246.55	$246.60
Purchase #2	$147.78	9.228%	$161.4171	$161.42	$161.40	$161.40
Purchase #3	$82.63	7.856%	$89.1214	$89.12	$89.10	$89.10
Purchase #4	$242.96	12.724%	$273.8742	$273.87	$273.85	$273.90
Purchase #5	$243.80	10.187%	$268.6359	$268.64	$268.65	$268.60
Purchase #6	$72.74	6.144%	$77.2091	$77.21	$77.20	$77.20
Purchase #7	$31.41	6.668%	$33.5044	$33.50	$33.50	$33.50
7 purchase totals =	$1,052.15		$1,150.3185	$1,150.32	$1,150.25	$1,150.30