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	$226.56	3.523%	$234.5417	$234.54	$234.55	$234.50
Purchase #2	$197.71	7.310%	$212.1626	$212.16	$212.15	$212.20
Purchase #3	$28.85	10.483%	$31.8743	$31.87	$31.85	$31.90
Purchase #4	$209.54	6.215%	$222.5629	$222.56	$222.55	$222.60
Purchase #5	$38.33	12.254%	$43.027	$43.03	$43.05	$43.00
Purchase #6	$125.84	13.273%	$142.5427	$142.54	$142.55	$142.50
Purchase #7	$31.79	10.511%	$35.1314	$35.13	$35.15	$35.10
7 purchase totals =	$858.62		$921.8426	$921.83	$921.85	$921.80