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	$108.35	10.770%	$120.0193	$120.02	$120.00	$120.00
Purchase #2	$36.85	7.838%	$39.7383	$39.74	$39.75	$39.70
Purchase #3	$136.33	7.132%	$146.0531	$146.05	$146.05	$146.10
Purchase #4	$196.70	10.258%	$216.8775	$216.88	$216.90	$216.90
Purchase #5	$184.94	7.455%	$198.7273	$198.73	$198.75	$198.70
Purchase #6	$182.36	7.800%	$196.5841	$196.58	$196.60	$196.60
Purchase #7	$89.92	13.572%	$102.1239	$102.12	$102.10	$102.10
7 purchase totals =	$935.45		$1,020.1235	$1,020.12	$1,020.15	$1,020.10