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	$136.91	7.739%	$147.5055	$147.51	$147.50	$147.50
Purchase #2	$175.94	5.818%	$186.1762	$186.18	$186.20	$186.20
Purchase #3	$122.32	13.524%	$138.8626	$138.86	$138.85	$138.90
Purchase #4	$169.91	9.475%	$186.009	$186.01	$186.00	$186.00
Purchase #5	$157.78	5.166%	$165.9309	$165.93	$165.95	$165.90
Purchase #6	$123.73	3.169%	$127.651	$127.65	$127.65	$127.70
Purchase #7	$73.55	11.681%	$82.1414	$82.14	$82.15	$82.10
7 purchase totals =	$960.14		$1,034.2766	$1,034.28	$1,034.30	$1,034.30