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	$243.70	8.584%	$264.6192	$264.62	$264.60	$264.60
Purchase #2	$57.37	3.400%	$59.3206	$59.32	$59.30	$59.30
Purchase #3	$186.71	3.483%	$193.2131	$193.21	$193.20	$193.20
Purchase #4	$65.75	10.667%	$72.7636	$72.76	$72.75	$72.80
Purchase #5	$150.77	3.331%	$155.7921	$155.79	$155.80	$155.80
Purchase #6	$136.33	8.839%	$148.3802	$148.38	$148.40	$148.40
Purchase #7	$210.70	11.386%	$234.6903	$234.69	$234.70	$234.70
7 purchase totals =	$1,051.33		$1,128.7791	$1,128.77	$1,128.75	$1,128.80