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	$165.30	8.342%	$179.0893	$179.09	$179.10	$179.10
Purchase #2	$249.90	7.299%	$268.1402	$268.14	$268.15	$268.10
Purchase #3	$187.85	8.500%	$203.8173	$203.82	$203.80	$203.80
Purchase #4	$218.83	10.203%	$241.1572	$241.16	$241.15	$241.20
Purchase #5	$109.33	9.341%	$119.5425	$119.54	$119.55	$119.50
Purchase #6	$93.53	7.860%	$100.8815	$100.88	$100.90	$100.90
Purchase #7	$207.65	7.816%	$223.8799	$223.88	$223.90	$223.90
7 purchase totals =	$1,232.39		$1,336.5079	$1,336.51	$1,336.55	$1,336.50