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	$107.32	6.582%	$114.3838	$114.38	$114.40	$114.40
Purchase #2	$59.72	4.755%	$62.5597	$62.56	$62.55	$62.60
Purchase #3	$65.53	11.288%	$72.927	$72.93	$72.95	$72.90
Purchase #4	$27.90	7.416%	$29.9691	$29.97	$29.95	$30.00
Purchase #5	$139.84	5.676%	$147.7773	$147.78	$147.80	$147.80
Purchase #6	$52.79	4.201%	$55.0077	$55.01	$55.00	$55.00
Purchase #7	$84.69	6.474%	$90.1728	$90.17	$90.15	$90.20
7 purchase totals =	$537.79		$572.7974	$572.80	$572.80	$572.90