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	$185.94	6.735%	$198.4631	$198.46	$198.45	$198.50
Purchase #2	$120.67	3.515%	$124.9116	$124.91	$124.90	$124.90
Purchase #3	$25.93	11.140%	$28.8186	$28.82	$28.80	$28.80
Purchase #4	$240.63	12.386%	$270.4344	$270.43	$270.45	$270.40
Purchase #5	$104.85	13.623%	$119.1337	$119.13	$119.15	$119.10
Purchase #6	$69.76	13.148%	$78.932	$78.93	$78.95	$78.90
Purchase #7	$233.93	9.441%	$256.0153	$256.02	$256.00	$256.00
7 purchase totals =	$981.71		$1,076.7087	$1,076.70	$1,076.70	$1,076.60