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	$112.33	7.675%	$120.9513	$120.95	$120.95	$121.00
Purchase #2	$128.74	7.557%	$138.4689	$138.47	$138.45	$138.50
Purchase #3	$237.56	13.194%	$268.9037	$268.90	$268.90	$268.90
Purchase #4	$98.55	13.488%	$111.8424	$111.84	$111.85	$111.80
Purchase #5	$152.79	12.131%	$171.325	$171.33	$171.35	$171.30
Purchase #6	$103.52	10.589%	$114.4817	$114.48	$114.50	$114.50
Purchase #7	$142.89	9.410%	$156.3359	$156.34	$156.35	$156.30
7 purchase totals =	$976.38		$1,082.3089	$1,082.31	$1,082.35	$1,082.30