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	$37.54	3.325%	$38.7882	$38.79	$38.80	$38.80
Purchase #2	$191.46	4.611%	$200.2882	$200.29	$200.30	$200.30
Purchase #3	$92.25	9.836%	$101.3237	$101.32	$101.30	$101.30
Purchase #4	$78.91	9.410%	$86.3354	$86.34	$86.35	$86.30
Purchase #5	$175.46	8.764%	$190.8373	$190.84	$190.85	$190.80
Purchase #6	$229.29	9.533%	$251.1482	$251.15	$251.15	$251.10
Purchase #7	$135.68	4.412%	$141.6662	$141.67	$141.65	$141.70
7 purchase totals =	$940.59		$1,010.3872	$1,010.40	$1,010.40	$1,010.30