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	$6.62	13.520%	$7.515	$7.52	$7.50	$7.50
Purchase #2	$150.72	9.221%	$164.6179	$164.62	$164.60	$164.60
Purchase #3	$96.42	7.144%	$103.3082	$103.31	$103.30	$103.30
Purchase #4	$149.46	12.103%	$167.5491	$167.55	$167.55	$167.50
Purchase #5	$207.90	10.135%	$228.9707	$228.97	$228.95	$229.00
Purchase #6	$201.44	13.444%	$228.5216	$228.52	$228.50	$228.50
Purchase #7	$245.48	11.838%	$274.5399	$274.54	$274.55	$274.50
7 purchase totals =	$1,058.04		$1,175.0224	$1,175.03	$1,174.95	$1,174.90