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	$116.95	3.661%	$121.2315	$121.23	$121.25	$121.20
Purchase #2	$232.61	7.830%	$250.8234	$250.82	$250.80	$250.80
Purchase #3	$247.41	13.290%	$280.2908	$280.29	$280.30	$280.30
Purchase #4	$231.54	4.294%	$241.4823	$241.48	$241.50	$241.50
Purchase #5	$136.64	10.305%	$150.7208	$150.72	$150.70	$150.70
Purchase #6	$96.38	3.230%	$99.4931	$99.49	$99.50	$99.50
Purchase #7	$58.56	4.696%	$61.31	$61.31	$61.30	$61.30
7 purchase totals =	$1,120.09		$1,205.3519	$1,205.34	$1,205.35	$1,205.30