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	$79.81	4.872%	$83.6983	$83.70	$83.70	$83.70
Purchase #2	$82.85	12.453%	$93.1673	$93.17	$93.15	$93.20
Purchase #3	$37.44	6.326%	$39.8085	$39.81	$39.80	$39.80
Purchase #4	$64.43	11.761%	$72.0076	$72.01	$72.00	$72.00
Purchase #5	$73.96	6.199%	$78.5448	$78.54	$78.55	$78.50
Purchase #6	$72.79	11.416%	$81.0997	$81.10	$81.10	$81.10
Purchase #7	$87.55	8.344%	$94.8552	$94.86	$94.85	$94.90
7 purchase totals =	$498.83		$543.1814	$543.19	$543.15	$543.20