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	$34.53	9.520%	$37.8173	$37.82	$37.80	$37.80
Purchase #2	$74.63	5.571%	$78.7876	$78.79	$78.80	$78.80
Purchase #3	$215.52	6.488%	$229.5029	$229.50	$229.50	$229.50
Purchase #4	$101.59	11.266%	$113.0351	$113.04	$113.05	$113.00
Purchase #5	$185.75	13.438%	$210.7111	$210.71	$210.70	$210.70
Purchase #6	$208.47	11.301%	$232.0292	$232.03	$232.05	$232.00
Purchase #7	$96.38	4.600%	$100.8135	$100.81	$100.80	$100.80
7 purchase totals =	$916.87		$1,002.6967	$1,002.70	$1,002.70	$1,002.60