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	$150.62	12.474%	$169.4083	$169.41	$169.40	$169.40
Purchase #2	$176.51	12.264%	$198.1572	$198.16	$198.15	$198.20
Purchase #3	$77.48	3.556%	$80.2352	$80.24	$80.25	$80.20
Purchase #4	$48.78	12.302%	$54.7809	$54.78	$54.80	$54.80
Purchase #5	$101.37	9.531%	$111.0316	$111.03	$111.05	$111.00
Purchase #6	$165.94	3.501%	$171.7496	$171.75	$171.75	$171.70
Purchase #7	$78.62	10.378%	$86.7792	$86.78	$86.80	$86.80
7 purchase totals =	$799.32		$872.1420	$872.15	$872.20	$872.10