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	$235.29	12.309%	$264.2518	$264.25	$264.25	$264.30
Purchase #2	$97.43	3.525%	$100.8644	$100.86	$100.85	$100.90
Purchase #3	$77.35	3.692%	$80.2058	$80.21	$80.20	$80.20
Purchase #4	$32.80	7.529%	$35.2695	$35.27	$35.25	$35.30
Purchase #5	$36.41	13.432%	$41.3006	$41.30	$41.30	$41.30
Purchase #6	$131.98	6.107%	$140.04	$140.04	$140.05	$140.00
Purchase #7	$169.77	12.401%	$190.8232	$190.82	$190.80	$190.80
7 purchase totals =	$781.03		$852.7553	$852.75	$852.70	$852.80