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	$37.32	4.270%	$38.9136	$38.91	$38.90	$38.90
Purchase #2	$90.91	6.195%	$96.5419	$96.54	$96.55	$96.50
Purchase #3	$243.36	12.496%	$273.7703	$273.77	$273.75	$273.80
Purchase #4	$233.44	13.475%	$264.896	$264.90	$264.90	$264.90
Purchase #5	$54.28	9.338%	$59.3487	$59.35	$59.35	$59.30
Purchase #6	$148.40	11.117%	$164.8976	$164.90	$164.90	$164.90
Purchase #7	$185.42	9.676%	$203.3612	$203.36	$203.35	$203.40
7 purchase totals =	$993.13		$1,101.7293	$1,101.73	$1,101.70	$1,101.70