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	$240.59	12.588%	$270.8755	$270.88	$270.90	$270.90
Purchase #2	$236.75	11.329%	$263.5714	$263.57	$263.55	$263.60
Purchase #3	$88.38	13.745%	$100.5278	$100.53	$100.55	$100.50
Purchase #4	$187.89	11.791%	$210.0441	$210.04	$210.05	$210.00
Purchase #5	$79.93	6.814%	$85.3764	$85.38	$85.40	$85.40
Purchase #6	$104.84	7.197%	$112.3853	$112.39	$112.40	$112.40
Purchase #7	$78.74	6.428%	$83.8014	$83.80	$83.80	$83.80
7 purchase totals =	$1,017.12		$1,126.5819	$1,126.59	$1,126.65	$1,126.60