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	$100.85	9.222%	$110.1504	$110.15	$110.15	$110.20
Purchase #2	$43.73	4.517%	$45.7053	$45.71	$45.70	$45.70
Purchase #3	$21.72	11.590%	$24.2373	$24.24	$24.25	$24.20
Purchase #4	$27.67	12.874%	$31.2322	$31.23	$31.25	$31.20
Purchase #5	$64.55	11.823%	$72.1817	$72.18	$72.20	$72.20
Purchase #6	$111.74	6.515%	$119.0199	$119.02	$119.00	$119.00
Purchase #7	$209.94	11.140%	$233.3273	$233.33	$233.35	$233.30
7 purchase totals =	$580.20		$635.8541	$635.86	$635.90	$635.80