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	$55.26	6.851%	$59.0459	$59.05	$59.05	$59.00
Purchase #2	$72.31	12.464%	$81.3227	$81.32	$81.30	$81.30
Purchase #3	$64.42	10.406%	$71.1235	$71.12	$71.10	$71.10
Purchase #4	$152.84	10.658%	$169.1297	$169.13	$169.15	$169.10
Purchase #5	$210.52	8.514%	$228.4437	$228.44	$228.45	$228.40
Purchase #6	$116.72	5.386%	$123.0065	$123.01	$123.00	$123.00
Purchase #7	$160.73	8.334%	$174.1252	$174.13	$174.15	$174.10
7 purchase totals =	$832.80		$906.1972	$906.20	$906.20	$906.00