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	$203.51	13.703%	$231.397	$231.40	$231.40	$231.40
Purchase #2	$240.75	12.700%	$271.3253	$271.33	$271.35	$271.30
Purchase #3	$147.74	13.729%	$168.0232	$168.02	$168.00	$168.00
Purchase #4	$216.98	8.713%	$235.8855	$235.89	$235.90	$235.90
Purchase #5	$92.54	11.454%	$103.1395	$103.14	$103.15	$103.10
Purchase #6	$187.90	6.824%	$200.7223	$200.72	$200.70	$200.70
Purchase #7	$135.56	10.828%	$150.2384	$150.24	$150.25	$150.20
7 purchase totals =	$1,224.98		$1,360.7312	$1,360.74	$1,360.75	$1,360.60