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	$38.99	3.582%	$40.3866	$40.39	$40.40	$40.40
Purchase #2	$79.89	3.327%	$82.5479	$82.55	$82.55	$82.50
Purchase #3	$201.28	7.148%	$215.6675	$215.67	$215.65	$215.70
Purchase #4	$166.67	9.258%	$182.1003	$182.10	$182.10	$182.10
Purchase #5	$240.44	13.867%	$273.7818	$273.78	$273.80	$273.80
Purchase #6	$150.40	10.476%	$166.1559	$166.16	$166.15	$166.20
Purchase #7	$118.28	10.818%	$131.0755	$131.08	$131.10	$131.10
7 purchase totals =	$995.95		$1,091.7155	$1,091.73	$1,091.75	$1,091.80