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	$65.30	12.358%	$73.3698	$73.37	$73.35	$73.40
Purchase #2	$53.55	11.142%	$59.5165	$59.52	$59.50	$59.50
Purchase #3	$178.44	5.673%	$188.5629	$188.56	$188.55	$188.60
Purchase #4	$171.64	10.681%	$189.9729	$189.97	$189.95	$190.00
Purchase #5	$81.45	9.832%	$89.4582	$89.46	$89.45	$89.50
Purchase #6	$47.30	6.797%	$50.515	$50.52	$50.50	$50.50
Purchase #7	$247.30	10.597%	$273.5064	$273.51	$273.50	$273.50
7 purchase totals =	$844.98		$924.9017	$924.91	$924.80	$925.00