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	$178.91	3.682%	$185.4975	$185.50	$185.50	$185.50
Purchase #2	$34.38	11.152%	$38.2141	$38.21	$38.20	$38.20
Purchase #3	$68.46	11.373%	$76.246	$76.25	$76.25	$76.20
Purchase #4	$38.91	12.581%	$43.8053	$43.81	$43.80	$43.80
Purchase #5	$79.56	13.360%	$90.1892	$90.19	$90.20	$90.20
Purchase #6	$165.96	3.414%	$171.6259	$171.63	$171.65	$171.60
Purchase #7	$184.61	10.809%	$204.5645	$204.56	$204.55	$204.60
7 purchase totals =	$750.79		$810.1425	$810.15	$810.15	$810.10