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	$124.83	8.264%	$135.146	$135.15	$135.15	$135.10
Purchase #2	$71.56	13.425%	$81.1669	$81.17	$81.15	$81.20
Purchase #3	$198.57	4.181%	$206.8722	$206.87	$206.85	$206.90
Purchase #4	$55.85	9.231%	$61.0055	$61.01	$61.00	$61.00
Purchase #5	$53.34	10.701%	$59.0479	$59.05	$59.05	$59.00
Purchase #6	$198.74	6.131%	$210.9247	$210.92	$210.90	$210.90
Purchase #7	$237.92	5.200%	$250.2918	$250.29	$250.30	$250.30
7 purchase totals =	$940.81		$1,004.4550	$1,004.46	$1,004.40	$1,004.40