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	$249.42	9.512%	$273.1448	$273.14	$273.15	$273.10
Purchase #2	$84.93	6.353%	$90.3256	$90.33	$90.35	$90.30
Purchase #3	$232.94	7.323%	$249.9982	$250.00	$250.00	$250.00
Purchase #4	$86.32	3.524%	$89.3619	$89.36	$89.35	$89.40
Purchase #5	$165.44	8.450%	$179.4197	$179.42	$179.40	$179.40
Purchase #6	$40.56	3.628%	$42.0315	$42.03	$42.05	$42.00
Purchase #7	$82.37	6.215%	$87.4893	$87.49	$87.50	$87.50
7 purchase totals =	$941.98		$1,011.7710	$1,011.77	$1,011.80	$1,011.70