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	$123.44	3.133%	$127.3074	$127.31	$127.30	$127.30
Purchase #2	$96.41	12.598%	$108.5557	$108.56	$108.55	$108.60
Purchase #3	$184.25	12.829%	$207.8874	$207.89	$207.90	$207.90
Purchase #4	$121.33	11.218%	$134.9408	$134.94	$134.95	$134.90
Purchase #5	$206.49	8.148%	$223.3148	$223.31	$223.30	$223.30
Purchase #6	$135.29	5.220%	$142.3521	$142.35	$142.35	$142.40
Purchase #7	$156.49	5.545%	$165.1674	$165.17	$165.15	$165.20
7 purchase totals =	$1,023.70		$1,109.5256	$1,109.53	$1,109.50	$1,109.60