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	$231.91	7.280%	$248.793	$248.79	$248.80	$248.80
Purchase #2	$139.82	9.238%	$152.7366	$152.74	$152.75	$152.70
Purchase #3	$82.51	7.292%	$88.5266	$88.53	$88.55	$88.50
Purchase #4	$102.79	5.458%	$108.4003	$108.40	$108.40	$108.40
Purchase #5	$168.88	3.114%	$174.1389	$174.14	$174.15	$174.10
Purchase #6	$181.25	10.573%	$200.4136	$200.41	$200.40	$200.40
Purchase #7	$105.38	12.831%	$118.9013	$118.90	$118.90	$118.90
7 purchase totals =	$1,012.54		$1,091.9103	$1,091.91	$1,091.95	$1,091.80