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	$245.53	12.454%	$276.1083	$276.11	$276.10	$276.10
Purchase #2	$81.53	13.335%	$92.402	$92.40	$92.40	$92.40
Purchase #3	$142.86	5.694%	$150.9944	$150.99	$151.00	$151.00
Purchase #4	$33.59	4.690%	$35.1654	$35.17	$35.15	$35.20
Purchase #5	$147.78	11.316%	$164.5028	$164.50	$164.50	$164.50
Purchase #6	$42.40	3.482%	$43.8764	$43.88	$43.90	$43.90
Purchase #7	$90.35	12.738%	$101.8588	$101.86	$101.85	$101.90
7 purchase totals =	$784.04		$864.9081	$864.91	$864.90	$865.00