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	$129.89	9.696%	$142.4841	$142.48	$142.50	$142.50
Purchase #2	$65.41	10.331%	$72.1675	$72.17	$72.15	$72.20
Purchase #3	$206.71	13.789%	$235.2132	$235.21	$235.20	$235.20
Purchase #4	$204.73	5.172%	$215.3186	$215.32	$215.30	$215.30
Purchase #5	$64.48	5.404%	$67.9645	$67.96	$67.95	$68.00
Purchase #6	$100.63	4.397%	$105.0547	$105.05	$105.05	$105.10
Purchase #7	$82.38	4.856%	$86.3804	$86.38	$86.40	$86.40
7 purchase totals =	$854.23		$924.5830	$924.57	$924.55	$924.70