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	$89.42	10.484%	$98.7948	$98.79	$98.80	$98.80
Purchase #2	$70.86	9.395%	$77.5173	$77.52	$77.50	$77.50
Purchase #3	$223.94	7.252%	$240.1801	$240.18	$240.20	$240.20
Purchase #4	$147.79	13.831%	$168.2308	$168.23	$168.25	$168.20
Purchase #5	$57.75	3.742%	$59.911	$59.91	$59.90	$59.90
Purchase #6	$198.31	8.787%	$215.7355	$215.74	$215.75	$215.70
Purchase #7	$196.55	11.291%	$218.7425	$218.74	$218.75	$218.70
7 purchase totals =	$984.62		$1,079.1120	$1,079.11	$1,079.15	$1,079.00