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	$37.38	13.202%	$42.3149	$42.31	$42.30	$42.30
Purchase #2	$110.40	7.811%	$119.0233	$119.02	$119.00	$119.00
Purchase #3	$242.74	11.436%	$270.4997	$270.50	$270.50	$270.50
Purchase #4	$174.80	13.581%	$198.5396	$198.54	$198.55	$198.50
Purchase #5	$84.71	6.784%	$90.4567	$90.46	$90.45	$90.50
Purchase #6	$165.69	8.321%	$179.4771	$179.48	$179.50	$179.50
Purchase #7	$70.84	3.866%	$73.5787	$73.58	$73.60	$73.60
7 purchase totals =	$886.56		$973.8900	$973.89	$973.90	$973.90