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	$249.44	8.374%	$270.3281	$270.33	$270.35	$270.30
Purchase #2	$67.90	7.359%	$72.8968	$72.90	$72.90	$72.90
Purchase #3	$145.45	13.357%	$164.8778	$164.88	$164.90	$164.90
Purchase #4	$130.83	5.731%	$138.3279	$138.33	$138.35	$138.30
Purchase #5	$205.40	11.713%	$229.4585	$229.46	$229.45	$229.50
Purchase #6	$191.48	10.644%	$211.8611	$211.86	$211.85	$211.90
Purchase #7	$26.32	4.150%	$27.4123	$27.41	$27.40	$27.40
7 purchase totals =	$1,016.82		$1,115.1625	$1,115.17	$1,115.20	$1,115.20