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	$140.53	3.269%	$145.1239	$145.12	$145.10	$145.10
Purchase #2	$85.49	10.448%	$94.422	$94.42	$94.40	$94.40
Purchase #3	$176.34	3.639%	$182.757	$182.76	$182.75	$182.80
Purchase #4	$90.70	10.164%	$99.9187	$99.92	$99.90	$99.90
Purchase #5	$179.88	3.686%	$186.5104	$186.51	$186.50	$186.50
Purchase #6	$85.74	8.619%	$93.1299	$93.13	$93.15	$93.10
Purchase #7	$82.82	10.322%	$91.3687	$91.37	$91.35	$91.40
7 purchase totals =	$841.50		$893.2306	$893.23	$893.15	$893.20