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	$178.82	7.127%	$191.5645	$191.56	$191.55	$191.60
Purchase #2	$40.80	3.746%	$42.3284	$42.33	$42.35	$42.30
Purchase #3	$213.25	4.814%	$223.5159	$223.52	$223.50	$223.50
Purchase #4	$5.97	12.829%	$6.7359	$6.74	$6.75	$6.70
Purchase #5	$215.45	9.300%	$235.4869	$235.49	$235.50	$235.50
Purchase #6	$48.98	13.815%	$55.7466	$55.75	$55.75	$55.70
Purchase #7	$57.33	7.336%	$61.5357	$61.54	$61.55	$61.50
7 purchase totals =	$760.60		$816.9139	$816.93	$816.95	$816.80