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	$249.53	12.702%	$281.2253	$281.23	$281.25	$281.20
Purchase #2	$186.96	3.474%	$193.455	$193.46	$193.45	$193.50
Purchase #3	$128.92	10.609%	$142.5971	$142.60	$142.60	$142.60
Purchase #4	$115.94	7.251%	$124.3468	$124.35	$124.35	$124.30
Purchase #5	$58.73	3.333%	$60.6875	$60.69	$60.70	$60.70
Purchase #6	$80.90	10.544%	$89.4301	$89.43	$89.45	$89.40
Purchase #7	$127.74	11.557%	$142.5029	$142.50	$142.50	$142.50
7 purchase totals =	$948.72		$1,034.2447	$1,034.26	$1,034.30	$1,034.20