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	$76.41	9.308%	$83.5222	$83.52	$83.50	$83.50
Purchase #2	$184.76	8.633%	$200.7103	$200.71	$200.70	$200.70
Purchase #3	$6.56	8.158%	$7.0952	$7.10	$7.10	$7.10
Purchase #4	$69.54	9.855%	$76.3932	$76.39	$76.40	$76.40
Purchase #5	$102.46	3.840%	$106.3945	$106.39	$106.40	$106.40
Purchase #6	$31.76	12.687%	$35.7894	$35.79	$35.80	$35.80
Purchase #7	$39.37	6.375%	$41.8798	$41.88	$41.90	$41.90
7 purchase totals =	$510.86		$551.7846	$551.78	$551.80	$551.80