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	$115.88	13.603%	$131.6432	$131.64	$131.65	$131.60
Purchase #2	$111.52	13.695%	$126.7927	$126.79	$126.80	$126.80
Purchase #3	$86.77	12.791%	$97.8688	$97.87	$97.85	$97.90
Purchase #4	$245.33	13.681%	$278.8936	$278.89	$278.90	$278.90
Purchase #5	$242.46	10.276%	$267.3752	$267.38	$267.40	$267.40
Purchase #6	$70.29	5.215%	$73.9556	$73.96	$73.95	$74.00
Purchase #7	$31.85	3.340%	$32.9138	$32.91	$32.90	$32.90
7 purchase totals =	$904.10		$1,009.4429	$1,009.44	$1,009.45	$1,009.50