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	$151.34	8.722%	$164.5399	$164.54	$164.55	$164.50
Purchase #2	$125.47	4.240%	$130.7899	$130.79	$130.80	$130.80
Purchase #3	$124.79	12.449%	$140.3251	$140.33	$140.35	$140.30
Purchase #4	$39.96	9.322%	$43.6851	$43.69	$43.70	$43.70
Purchase #5	$238.58	13.581%	$270.9815	$270.98	$271.00	$271.00
Purchase #6	$31.57	3.517%	$32.6803	$32.68	$32.70	$32.70
Purchase #7	$236.84	7.803%	$255.3206	$255.32	$255.30	$255.30
7 purchase totals =	$948.55		$1,038.3224	$1,038.33	$1,038.40	$1,038.30