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	$176.50	6.467%	$187.9143	$187.91	$187.90	$187.90
Purchase #2	$234.68	13.830%	$267.1362	$267.14	$267.15	$267.10
Purchase #3	$165.56	8.270%	$179.2518	$179.25	$179.25	$179.30
Purchase #4	$93.91	10.799%	$104.0513	$104.05	$104.05	$104.10
Purchase #5	$201.48	10.229%	$222.0894	$222.09	$222.10	$222.10
Purchase #6	$71.53	9.695%	$78.4648	$78.46	$78.45	$78.50
Purchase #7	$184.98	10.112%	$203.6852	$203.69	$203.70	$203.70
7 purchase totals =	$1,128.64		$1,242.5930	$1,242.59	$1,242.60	$1,242.70