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	$245.36	9.427%	$268.4901	$268.49	$268.50	$268.50
Purchase #2	$73.78	13.238%	$83.547	$83.55	$83.55	$83.50
Purchase #3	$95.33	9.129%	$104.0327	$104.03	$104.05	$104.00
Purchase #4	$35.37	7.580%	$38.051	$38.05	$38.05	$38.10
Purchase #5	$209.70	10.490%	$231.6975	$231.70	$231.70	$231.70
Purchase #6	$135.49	4.268%	$141.2727	$141.27	$141.25	$141.30
Purchase #7	$221.59	5.202%	$233.1171	$233.12	$233.10	$233.10
7 purchase totals =	$1,016.62		$1,100.2081	$1,100.21	$1,100.20	$1,100.20