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	$243.55	12.495%	$273.9816	$273.98	$274.00	$274.00
Purchase #2	$128.71	10.592%	$142.343	$142.34	$142.35	$142.30
Purchase #3	$105.36	4.316%	$109.9073	$109.91	$109.90	$109.90
Purchase #4	$189.48	5.773%	$200.4187	$200.42	$200.40	$200.40
Purchase #5	$33.53	11.851%	$37.5036	$37.50	$37.50	$37.50
Purchase #6	$179.55	13.542%	$203.8647	$203.86	$203.85	$203.90
Purchase #7	$177.85	7.191%	$190.6392	$190.64	$190.65	$190.60
7 purchase totals =	$1,058.03		$1,158.6581	$1,158.65	$1,158.65	$1,158.60