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	$67.27	6.166%	$71.4179	$71.42	$71.40	$71.40
Purchase #2	$136.71	10.143%	$150.5765	$150.58	$150.60	$150.60
Purchase #3	$185.91	6.649%	$198.2712	$198.27	$198.25	$198.30
Purchase #4	$91.30	7.698%	$98.3283	$98.33	$98.35	$98.30
Purchase #5	$169.72	6.711%	$181.1099	$181.11	$181.10	$181.10
Purchase #6	$200.88	7.850%	$216.6491	$216.65	$216.65	$216.60
Purchase #7	$187.91	9.359%	$205.4965	$205.50	$205.50	$205.50
7 purchase totals =	$1,039.70		$1,121.8494	$1,121.86	$1,121.85	$1,121.80