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	$83.62	12.144%	$93.7748	$93.77	$93.75	$93.80
Purchase #2	$125.62	11.751%	$140.3816	$140.38	$140.40	$140.40
Purchase #3	$209.90	9.352%	$229.5298	$229.53	$229.55	$229.50
Purchase #4	$84.82	4.833%	$88.9194	$88.92	$88.90	$88.90
Purchase #5	$50.72	8.167%	$54.8623	$54.86	$54.85	$54.90
Purchase #6	$95.49	4.490%	$99.7775	$99.78	$99.80	$99.80
Purchase #7	$116.72	6.648%	$124.4795	$124.48	$124.50	$124.50
7 purchase totals =	$766.89		$831.7249	$831.72	$831.75	$831.80