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	$204.54	8.299%	$221.5148	$221.51	$221.50	$221.50
Purchase #2	$182.25	5.151%	$191.6377	$191.64	$191.65	$191.60
Purchase #3	$80.64	6.385%	$85.7889	$85.79	$85.80	$85.80
Purchase #4	$250.96	7.797%	$270.5274	$270.53	$270.55	$270.50
Purchase #5	$196.50	11.603%	$219.2999	$219.30	$219.30	$219.30
Purchase #6	$104.42	4.831%	$109.4645	$109.46	$109.45	$109.50
Purchase #7	$159.90	9.478%	$175.0553	$175.06	$175.05	$175.10
7 purchase totals =	$1,179.21		$1,273.2885	$1,273.29	$1,273.30	$1,273.30