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	$119.77	9.469%	$131.111	$131.11	$131.10	$131.10
Purchase #2	$198.28	11.706%	$221.4907	$221.49	$221.50	$221.50
Purchase #3	$141.71	12.543%	$159.4847	$159.48	$159.50	$159.50
Purchase #4	$139.89	5.800%	$148.0036	$148.00	$148.00	$148.00
Purchase #5	$38.69	10.655%	$42.8124	$42.81	$42.80	$42.80
Purchase #6	$232.59	11.744%	$259.9054	$259.91	$259.90	$259.90
Purchase #7	$169.87	10.851%	$188.3026	$188.30	$188.30	$188.30
7 purchase totals =	$1,040.80		$1,151.1104	$1,151.10	$1,151.10	$1,151.10