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	$99.25	13.619%	$112.7669	$112.77	$112.75	$112.80
Purchase #2	$133.70	11.696%	$149.3376	$149.34	$149.35	$149.30
Purchase #3	$189.86	12.639%	$213.8564	$213.86	$213.85	$213.90
Purchase #4	$172.73	10.773%	$191.3382	$191.34	$191.35	$191.30
Purchase #5	$39.36	7.156%	$42.1766	$42.18	$42.20	$42.20
Purchase #6	$175.33	3.238%	$181.0072	$181.01	$181.00	$181.00
Purchase #7	$169.61	11.296%	$188.7691	$188.77	$188.75	$188.80
7 purchase totals =	$979.84		$1,079.2520	$1,079.27	$1,079.25	$1,079.30