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	$174.31	8.301%	$188.7795	$188.78	$188.80	$188.80
Purchase #2	$36.81	3.704%	$38.1734	$38.17	$38.15	$38.20
Purchase #3	$185.84	3.220%	$191.824	$191.82	$191.80	$191.80
Purchase #4	$161.32	6.503%	$171.8106	$171.81	$171.80	$171.80
Purchase #5	$38.77	4.512%	$40.5193	$40.52	$40.50	$40.50
Purchase #6	$184.77	4.410%	$192.9184	$192.92	$192.90	$192.90
Purchase #7	$42.78	11.587%	$47.7369	$47.74	$47.75	$47.70
7 purchase totals =	$824.60		$871.7621	$871.76	$871.70	$871.70