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	$70.91	10.760%	$78.5399	$78.54	$78.55	$78.50
Purchase #2	$123.98	3.828%	$128.726	$128.73	$128.75	$128.70
Purchase #3	$165.38	9.807%	$181.5988	$181.60	$181.60	$181.60
Purchase #4	$83.39	7.138%	$89.3424	$89.34	$89.35	$89.30
Purchase #5	$97.59	12.714%	$109.9976	$110.00	$110.00	$110.00
Purchase #6	$95.42	4.258%	$99.483	$99.48	$99.50	$99.50
Purchase #7	$88.51	7.249%	$94.9261	$94.93	$94.95	$94.90
7 purchase totals =	$725.18		$782.6138	$782.62	$782.70	$782.50