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	$123.40	6.435%	$131.3408	$131.34	$131.35	$131.30
Purchase #2	$36.56	7.678%	$39.3671	$39.37	$39.35	$39.40
Purchase #3	$47.83	11.507%	$53.3338	$53.33	$53.35	$53.30
Purchase #4	$195.38	7.610%	$210.2484	$210.25	$210.25	$210.20
Purchase #5	$172.34	5.107%	$181.1414	$181.14	$181.15	$181.10
Purchase #6	$17.45	13.608%	$19.8246	$19.82	$19.80	$19.80
Purchase #7	$67.92	6.701%	$72.4713	$72.47	$72.45	$72.50
7 purchase totals =	$660.88		$707.7274	$707.72	$707.70	$707.60