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	$157.57	7.839%	$169.9219	$169.92	$169.90	$169.90
Purchase #2	$93.71	11.846%	$104.8109	$104.81	$104.80	$104.80
Purchase #3	$100.33	9.632%	$109.9938	$109.99	$110.00	$110.00
Purchase #4	$31.79	10.842%	$35.2367	$35.24	$35.25	$35.20
Purchase #5	$92.73	8.448%	$100.5638	$100.56	$100.55	$100.60
Purchase #6	$109.40	6.257%	$116.2452	$116.25	$116.25	$116.20
Purchase #7	$229.25	6.193%	$243.4475	$243.45	$243.45	$243.40
7 purchase totals =	$814.78		$880.2198	$880.22	$880.20	$880.10