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	$81.32	9.710%	$89.2162	$89.22	$89.20	$89.20
Purchase #2	$150.86	11.454%	$168.1395	$168.14	$168.15	$168.10
Purchase #3	$77.42	12.346%	$86.9783	$86.98	$87.00	$87.00
Purchase #4	$52.64	12.140%	$59.0305	$59.03	$59.05	$59.00
Purchase #5	$243.58	13.751%	$277.0747	$277.07	$277.05	$277.10
Purchase #6	$98.36	12.299%	$110.4573	$110.46	$110.45	$110.50
Purchase #7	$203.52	8.790%	$221.4094	$221.41	$221.40	$221.40
7 purchase totals =	$907.70		$1,012.3059	$1,012.31	$1,012.30	$1,012.30