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	$118.80	10.576%	$131.3643	$131.36	$131.35	$131.40
Purchase #2	$64.58	4.618%	$67.5623	$67.56	$67.55	$67.60
Purchase #3	$122.47	5.234%	$128.8801	$128.88	$128.90	$128.90
Purchase #4	$229.46	7.128%	$245.8159	$245.82	$245.80	$245.80
Purchase #5	$39.87	13.696%	$45.3306	$45.33	$45.35	$45.30
Purchase #6	$86.41	8.815%	$94.027	$94.03	$94.05	$94.00
Purchase #7	$226.41	7.120%	$242.5304	$242.53	$242.55	$242.50
7 purchase totals =	$888.00		$955.5106	$955.51	$955.55	$955.50