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	$243.96	11.586%	$272.2252	$272.23	$272.25	$272.20
Purchase #2	$74.57	13.369%	$84.5393	$84.54	$84.55	$84.50
Purchase #3	$80.82	9.339%	$88.3678	$88.37	$88.35	$88.40
Purchase #4	$79.33	3.452%	$82.0685	$82.07	$82.05	$82.10
Purchase #5	$142.32	5.428%	$150.0451	$150.05	$150.05	$150.00
Purchase #6	$220.57	4.264%	$229.9751	$229.98	$230.00	$230.00
Purchase #7	$37.72	13.697%	$42.8865	$42.89	$42.90	$42.90
7 purchase totals =	$879.29		$950.1075	$950.13	$950.15	$950.10