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	$152.97	12.297%	$171.7807	$171.78	$171.80	$171.80
Purchase #2	$157.49	5.262%	$165.7771	$165.78	$165.80	$165.80
Purchase #3	$191.34	11.487%	$213.3192	$213.32	$213.30	$213.30
Purchase #4	$86.74	6.289%	$92.1951	$92.20	$92.20	$92.20
Purchase #5	$45.95	5.304%	$48.3872	$48.39	$48.40	$48.40
Purchase #6	$136.43	5.688%	$144.1901	$144.19	$144.20	$144.20
Purchase #7	$37.90	10.274%	$41.7938	$41.79	$41.80	$41.80
7 purchase totals =	$808.82		$877.4432	$877.45	$877.50	$877.50