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	$247.90	6.599%	$264.2589	$264.26	$264.25	$264.30
Purchase #2	$104.66	5.737%	$110.6643	$110.66	$110.65	$110.70
Purchase #3	$175.51	5.337%	$184.877	$184.88	$184.90	$184.90
Purchase #4	$96.82	13.436%	$109.8287	$109.83	$109.85	$109.80
Purchase #5	$169.54	6.179%	$180.0159	$180.02	$180.00	$180.00
Purchase #6	$75.34	9.309%	$82.3534	$82.35	$82.35	$82.40
Purchase #7	$148.29	8.469%	$160.8487	$160.85	$160.85	$160.80
7 purchase totals =	$1,018.06		$1,092.8469	$1,092.85	$1,092.85	$1,092.90