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	$83.26	9.268%	$90.9765	$90.98	$91.00	$91.00
Purchase #2	$220.61	12.557%	$248.312	$248.31	$248.30	$248.30
Purchase #3	$176.74	6.653%	$188.4985	$188.50	$188.50	$188.50
Purchase #4	$73.73	11.518%	$82.2222	$82.22	$82.20	$82.20
Purchase #5	$135.43	12.109%	$151.8292	$151.83	$151.85	$151.80
Purchase #6	$202.51	11.369%	$225.5334	$225.53	$225.55	$225.50
Purchase #7	$148.76	7.565%	$160.0137	$160.01	$160.00	$160.00
7 purchase totals =	$1,041.04		$1,147.3855	$1,147.38	$1,147.40	$1,147.30